Liquid-crystal medium

ABSTRACT

Disclosed are a liquid crystal (LC) medium containing a polymerisable compound, a process for its preparation, its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in an LC display of the polymer sustained alignment (PSA) type, and to an LC display, especially a PSA display.

The present invention relates to a liquid crystal (LC) medium comprising a polymerisable compound, to a process for its preparation, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in an LC display of the polymer sustained alignment (PSA) type, and to an LC display, especially a PSA display, comprising it.

BACKGROUND OF THE INVENTION

A liquid crystal display mode which has meanwhile found widespread interest and commercial use is the so-called PS (“polymer sustained”) or PSA (“polymer sustained alignment”) mode, for which the term “polymer stabilised” is also occasionally used. In PSA displays an LC medium is used that contains an LC mixture (hereinafter also referred to as “host mixture”) and a small amount, typically <1% by weight, for example 0.2 to 0.4% by weight, of one or more polymerisable compounds, preferably polymerisable monomeric compounds. After filling the LC medium into the display, the polymerisable compounds are polymerised or crosslinked in situ, usually by UV photopolymerisation, optionally while a voltage is applied to the electrodes of the display. The polymerisation is carried out at a temperature where the LC medium exhibits a liquid crystal phase, usually at room temperature. The addition of polymerisable mesogenic or liquid-crystalline compounds, also known as reactive mesogens or “RMs”, to the LC host mixture has proven particularly suitable.

The PS(A) mode is meanwhile used in various conventional LC display types. Thus, for example, PS-VA (“vertically aligned”), PS-OCB (“optically compensated bend”), PS-IPS (“in-plane switching”), PS-FFS (“fringe-field switching”), PS-UB-FFS (“Ultra Brightness FFS) and PS-TN (“twisted nematic”) displays are known. The polymerisation of the RMs preferably takes place with an applied voltage in the case of PS-VA and PS-OCB displays, and with or without, preferably without, an applied voltage in the case of PS-IPS displays. As a result a pretilt angle of the LC molecules is generated in the display cell. In case of PS-OCB displays, for example, it is possible for the bend structure to be stabilised so that an offset voltage is unnecessary or can be reduced. In case of PS-VA displays, the pretilt has a positive effect on the response times. For PS-VA displays, a standard MVA (“multidomain VA”) or PVA (“patterned VA”) pixel and electrode layout can be used. It is also possible to use only one structured electrode without protrusions, which significantly simplifies production and improves contrast and transparency.

Furthermore, the so-called posi-VA mode (“positive VA”) has proven to be particularly suitable. Like in conventional VA and PS-VA displays, the initial orientation of the LC molecules in posi-VA displays is homeotropic, i.e. substantially perpendicular to the substrates, in the initial state when no voltage is applied. However, in contrast to conventional VA and PS-VA displays, in posi-VA displays LC media with positive dielectric anisotropy are used. Like in IPS and PS-IPS displays, the two electrodes in posi-VA displays are arranged only on one of the two substrates, and preferably exhibit intermeshed, comb-shaped (interdigital) structures. Upon application of a voltage to the interdigital electrodes, which create an electrical field that is substantially parallel to the layer of the LC medium, the LC molecules are switched to an orientation substantially parallel to the substrates. In posi-VA displays, a polymer stabilisation by addition of RMs to the LC medium, which are then polymerised in the display, has also proven to be advantageous. Thereby a significant reduction of the switching times can be achieved.

PS-VA displays are described for example in EP1170626 A2, U.S. Pat. No. 6,861,107, U.S. Pat. No. 7,169,449, US2004/0191428A1, US2006/0066793A1 and US2006/0103804A1. PS-OCB displays are described for example in T.-J-Chen et al., Jpn. J. Appl. Phys. 45, 2006, 2702-2704 and S. H. Kim, L.-C-Chien, Jpn. J. Appl. Phys. 43, 2004, 7643-7647. PS-IPS displays are described for example in U.S. Pat. No. 6,177,972 and Appl. Phys. Lett. 1999, 75(21), 3264. PS-TN displays are described for example in Optics Express 2004, 12(7), 1221.

PSA displays can be operated as either active-matrix or passive-matrix displays. In case of active-matrix displays individual pixels are usually addressed by integrated, non-linear active elements like for example transistors (such as thin-film transistors or “TFTs”), whereas in passive-matrix displays individual pixels are usually addressed by the multiplex method as known from prior art.

A PSA display may also comprise an alignment layer on one or both of the substrates forming the display cell. The alignment layer is usually applied on the electrodes (in case such electrodes are present) such that it is in contact with the LC medium and induces initial alignment of the LC molecules. The alignment layer may comprise or consist of, for example, a polyimide, which may also be rubbed or prepared by a photoalignment method.

In particular for monitor and especially TV applications optimisation of the response times, but also of the contrast and luminance (and thus transmission) of the LC display is still desired. The PSA method can provide significant advantages here. Especially in case of PS-VA, PS-IPS, PS-FFS and PS-posi-VA displays, a shortening of the response times, which correlate with a measurable pretilt in test cells, can be achieved without significant adverse effects on other parameters.

Prior art has suggested biphenyl diacrylates or dimethacrylates, which are optionally fluorinated, as RMs for use in PSA displays

However, the problem arises that not all combinations of LC host mixture and RM(s) are suitable for use in PSA displays because, for example, only inadequate tilt angles or no tilt angles at all could be generated or because, for example, the voltage holding ratio (VHR) is inadequate for TFT display applications. In addition, it has been found that the LC mixtures and RMs known from prior art still have some disadvantages when used in PSA displays. Thus, not every known RM which is soluble in the LC host mixture is suitable for use in PSA displays. In addition, it is often difficult to find a suitable selection criterion for the RM besides direct measurement of the pretilt in the PSA display. The choice of suitable RMs becomes even smaller if UV photopolymerisation without the addition of photoinitiators is desired, which is advantageous for certain applications.

In addition, the selected combination of LC host mixture/RM should have a low rotational viscosity and good electrical properties, in particular a high VHR. In PSA displays, a high VHR after irradiation with UV light is particularly important, because UV exposure does not only occur as normal exposure during operation of the finished display, but is also a necessary part of the display production process.

In particular, it is desirable to have available improved materials for PSA displays which produce a particularly small pretilt angle. Preferred materials are those which, compared to prior art materials, can generate a lower pretilt angle after the same exposure time, and/or can generate at least the same pretilt angle after a shorter exposure time. This would allow to reduce the display production time (“tact time”) and production costs.

A further problem in the production of PSA displays is the presence and removal of residual amounts of unpolymerised RMs after the polymerisation step that is necessary for generation of the pretilt angle in the display. Unreacted RMs may adversely affect the properties of the display, for example by polymerising in an uncontrolled manner during display operation.

Thus, the PSA displays known from prior art often exhibit the undesired effect of so-called “image sticking” or “image burn”, i.e. the image produced in the LC display by temporary addressing of individual pixels still remains visible even after the electric field in these pixels has been switched off, or after other pixels have been addressed.

Image sticking can occur for example if LC host mixtures having a low VHR are used. The UV component of daylight or the display backlight can cause undesired decomposition reactions of the LC molecules and initiate the production of ionic or free-radical impurities. These can accumulate in particular at the electrodes or the alignment layers, where they reduce the effective applied voltage. This effect can also be observed in conventional LC displays without a polymer component.

An additional image sticking effect caused by the presence of unpolymerised RMs is often observed in PSA displays. Uncontrolled polymerisation of the residual RMs is initiated by UV light from the environment or the backlight. In the switched display areas, this changes the tilt angle after a number of addressing cycles. As a result, a change in transmission in the switched areas may occur, while it remains unchanged in the unswitched areas.

During production of the PSA display it is therefore desirable that polymerisation of the RMs proceeds as completely as possible and the presence of unpolymerised RMs in the display can be excluded or reduced to a minimum. Thus, RMs and LC host mixtures are required which enable or support quick and complete polymerisation of the RMs. In addition, a controlled reaction of the residual RM amounts is desirable. This could be achieved by providing improved RMs that polymerise quicker and more effectively than the RMs of prior art.

A further problem that has been observed in the operation of PSA displays is the stability of the pretilt angle. Thus, it was observed that the pretilt angle, which is generated during display manufacture by polymerising the RMs, does not remain constant but can deteriorate after the display was subjected to voltage stress during display operation. This can negatively affect the display performance, e.g. by increasing the black state transmission and hence lowering the contrast.

Another problem to be solved is that the RMs of prior art do often have high melting points, and do only show limited solubility in many commonly used LC mixtures. As a result the RMs tend to spontaneously crystallise out of the LC mixture. In addition, the risk of spontaneous polymerisation prevents that the LC host mixture can be warmed in order to better dissolve the RMs, so that a high solubility even at room temperature is required. In addition, there is a risk of phase separation, for example when filling the LC medium into the LC display (chromatography effect), which may greatly impair the homogeneity of the display. This is further aggravated by the fact that the LC media are usually filled in the display at low temperatures in order to reduce the risk of spontaneous polymerisation (see above), which in turn has an adverse effect on the solubility.

Another problem observed in prior art is that the use of conventional LC media in LC displays, including but not limited to displays of the PSA type, often leads to the occurrence of mura in the display, especially when the LC medium is filled in the display by using the one drop filling (ODF) method. This phenomenon is also known as “ODF mura”. It is therefore desirable to provide LC media which lead to reduced ODF mura.

Another problem observed in prior art is that LC media for use in PSA displays, including but not limited to displays of the PSA type, do often exhibit high viscosities and, as a consequence, high switching times. In order to reduce the viscosity and response time of the LC medium, it has been suggested in prior art to add LC compounds with an alkenyl group. However, it was observed that LC media containing alkenyl compounds often show a decrease of the reliability and stability, and a decrease of the VHR especially after exposure to UV radiation. Especially for use in PSA displays this is a considerable disadvantage, because the photo-polymerisation of the RMs in the PSA display is usually carried out by exposure to UV radiation, which may cause a VHR drop in the LC medium.

In prior art LC media for use in PSA displays have been proposed wherein the LC host mixture contains one or more terphenyl compounds in order to enhance polymerisation of the RMs. However, the addition of terphenyl compounds increases the viscosity of the LC host mixture, thus leading to slower response times. Besides the addition of terphenyl compounds can lead to reduced reliability and a drop of the VHR after UV stress in the LC medium.

It is therefore another problem to provide LC mixtures and LC media for PSA displays which show a reduced viscosity and a high VHR, while at the same time enabling quick and complete polymerisation of the RMs.

There is thus still a great demand for PSA displays and LC media and polymerisable compounds for use in such displays, which do not show the drawbacks as described above, or only do so to a small extent, and have improved properties.

In particular, there is a great demand for PSA displays, and LC mixtures and RMs for use in such PSA displays, which enable a high specific resistance at the same time as a large working-temperature range, short response times, even at low temperatures, a low threshold voltage, a low pretilt angle, a multiplicity of grey shades, high contrast and a broad viewing angle, high reliability and high values of the VHR after UV exposure, and, in case of the RMs, have low melting points and a high solubility in the LC host mixture. In PSA displays for mobile applications, it is especially desired to have available LC media that show low threshold voltage and high birefringence.

The invention is based on the object of providing novel suitable materials, in particular RMs, LC host mixtures, and LC media comprising the same, for use in PSA displays, which do not have the disadvantages indicated above or do so to a reduced extent.

In particular, the invention is based on the object of providing LC media for use in PSA displays, which enable very high specific resistance values, high VHR values, high reliability, low threshold voltages, short response times, high birefringence, show good UV absorption especially at longer wavelengths, allow quick and complete polymerisation of the RMs contained therein, allow the generation of a low pretilt angle as quickly as possible, enable a high stability of the pretilt even after longer time and/or after UV exposure, reduce or prevent the occurrence of image sticking in the display, and reduce or prevent the occurrence of ODF mura in the display.

Another object of the invention is to solve the problem of providing LC mixtures and LC media for PSA displays which show a reduced viscosity and a high VHR while enabling quick and complete polymerisation of the RMs.

The above objects have been achieved in accordance with the present invention by materials and processes as described and claimed in the present application.

It has surprisingly been found that at least some of the above-mentioned problems can be solved by using an LC medium comprising a polymerisable component and an LC host mixture containing compounds of formula A, B and T as disclosed and claimed hereinafter.

Thus it was found that, when using an LC medium as disclosed and claimed hereinafter in PSA displays, it is possible to lower the viscosity of the LC host mixture while still maintaining high VHR, high UV absorption which is needed for quick and complete polymerisation, and a strong tilt angle generation.

The use of LC media according to the present invention facilitates a quick and complete UV-photopolymerisation reaction in particular at low UV energy and/or longer UV wavelengths in the range from 300-380 nm and especially above 340 nm, which are considerable advantages for the display manufacturing process. Besides, the use of LC media according to the present invention allows a fast generation of large and stable pretilt angles, reduces image sticking and ODF mura in the display, leads to a high VHR value after UV photopolymerisation, and enables to achieve fast response times, a low threshold voltage and a high birefringence.

SUMMARY OF THE INVENTION

The invention relates to a liquid crystal (LC) medium comprising one or more polymerisable compounds, one or more compounds of formula A, one or more compounds of formula B and one or more compounds of formula T

in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:

-   R¹, R² alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms     or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are     optionally fluorinated, -   L¹, L², L³ F or Cl, preferably F.

The invention furthermore relates to an LC medium comprising

-   -   a polymerisable component A) comprising, preferably consisting         of, one or more polymerisable compounds, and     -   a liquid-crystalline component B), hereinafter also referred to         as “LC host mixture”, comprising, preferably consisting of, one         or more mesogenic or liquid-crystalline compounds, which         comprises one or more compounds of formula A, one or more         compounds of formula B and one or more compounds of formula T.

The liquid-crystalline component B) of an LC medium according to the present invention is hereinafter also referred to as “LC host mixture”, and preferably contains only LC compounds that are selected from low-molecular-weight compounds which are unpolymerisable, like those of formula A, B and T, and optionally contains additives like polymerisation initiators, inhibitors etc.

The invention furthermore relates to an LC medium or LC display as described above and below, wherein the polymerisable compounds of component A) are polymerised.

The invention furthermore relates to a process for preparing an LC medium as described above and below, comprising the steps of mixing one or more compounds of formula A, one or more compounds of formula B and one or more compounds of formula T Q, or an LC host mixture or LC component B) as described above and below, with one or more poylmerisable compounds, and optionally with further LC compounds and/or additives.

The invention further relates to the use of LC medium in LC displays, especially in PSA displays.

The invention furthermore relates to the use of LC medium according to the invention in PSA displays, in particular the use in PSA displays containing an LC medium, for the production of a tilt angle in the LC medium by in-situ polymerisation of the polymerisable compound(s) of component B) in the PSA display, preferably in an electric or magnetic field.

The invention furthermore relates to an LC display comprising one or more compounds of formula I or an LC medium according to the invention, in particular a PSA display, particularly preferably a PS-VA, PS-OCB, PS-IPS, PS-FFS, PS-UB-FFS, PS-posi-VA or PS-TN display.

The invention furthermore relates to an LC display comprising a polymer obtainable by polymerisation of one or more compounds of formula I or of a polymerisable component A) as described above, or comprising an LC medium according to the invention, which is preferably a PSA display, very preferably a PS-VA, PS-OCB, PS-IPS, PS-FFS, PS-UB-FFS, PS-posi-VA or PS-TN display.

The invention furthermore relates to an LC display of the PSA type comprising two substrates, at least one which is transparent to light, an electrode provided on each substrate or two electrodes provided on only one of the substrates, and located between the substrates a layer of an LC medium that comprises one or more polymerisable compounds and an LC component as described above and below, wherein the polymerisable compounds are polymerised between the substrates of the display.

The invention furthermore relates to a process for manufacturing an LC display as described above and below, comprising the steps of filling or otherwise providing an LC medium, which comprises one or more polymerisable compounds as described above and below, between the substrates of the display, and polymerising the polymerisable compounds.

The PSA displays according to the invention have two electrodes, preferably in the form of transparent layers, which are applied to one or both of the substrates. In some displays, for example in PS-VA, PS-OCB or PS-TN displays, one electrode is applied to each of the two substrates. In other displays, for example in PS-posi-VA, PS-IPS or PS-FFS or PS-UB-FFS displays, both electrodes are applied to only one of the two substrates.

In a preferred embodiment the polymerisable component is polymerised in the LC display while a voltage is applied to the electrodes of the display.

The polymerisable compounds of the polymerisable component are preferably polymerised by photo-polymerisation, very preferably by UV photo-polymerisation.

DETAILED DESCRIPTION OF THE INVENTION

Unless stated otherwise, the polymerisable compounds are preferably selected from achiral compounds.

As used herein, the terms “active layer” and “switchable layer” mean a layer in an electrooptical display, for example an LC display, that comprises one or more molecules having structural and optical anisotropy, like for example LC molecules, which change their orientation upon an external stimulus like an electric or magnetic field, resulting in a change of the transmission of the layer for polarized or unpolarized light.

As used herein, the terms “tilt” and “tilt angle” will be understood to mean a tilted alignment of the LC molecules of an LC medium relative to the surfaces of the cell in an LC display (here preferably a PSA display). The tilt angle here denotes the average angle (<90°) between the longitudinal molecular axes of the LC molecules (LC director) and the surface of the plane-parallel outer plates which form the LC cell. A low value for the tilt angle (i.e. a large deviation from the 90° angle) corresponds to a large tilt here. A suitable method for measurement of the tilt angle is given in the examples. Unless indicated otherwise, tilt angle values disclosed above and below relate to this measurement method.

As used herein, the terms “reactive mesogen” and “RM” will be understood to mean a compound containing a mesogenic or liquid crystalline skeleton, and one or more functional groups attached thereto which are suitable for polymerisation and are also referred to as “polymerisable group” or “P”.

Unless stated otherwise, the term “polymerisable compound” as used herein will be understood to mean a polymerisable monomeric compound.

As used herein, the term “low-molecular-weight compound” will be understood to mean to a compound that is monomeric and/or is not prepared by a polymerisation reaction, as opposed to a “polymeric compound” or a “polymer”.

As used herein, the term “unpolymerisable compound” will be understood to mean a compound that does not contain a functional group that is suitable for polymerisation under the conditions usually applied for the polymerisation of the RMs.

The term “mesogenic group” as used herein is known to the person skilled in the art and described in the literature, and means a group which, due to the anisotropy of its attracting and repelling interactions, essentially contributes to causing a liquid-crystal (LC) phase in low-molecular-weight or polymeric substances. Compounds containing mesogenic groups (mesogenic compounds) do not necessarily have to have an LC phase themselves. It is also possible for mesogenic compounds to exhibit LC phase behaviour only after mixing with other compounds and/or after polymerisation. Typical mesogenic groups are, for example, rigid rod- or disc-shaped units. An overview of the terms and definitions used in connection with mesogenic or LC compounds is given in Pure Appl. Chem. 2001, 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340-6368.

The term “spacer group”, hereinafter also referred to as “Sp”, as used herein is known to the person skilled in the art and is described in the literature, see, for example, Pure Appl. Chem. 2001, 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340-6368. As used herein, the terms “spacer group” or “spacer” mean a flexible group, for example an alkylene group, which connects the mesogenic group and the polymerisable group(s) in a polymerisable mesogenic compound.

Above and below,

denotes a trans-1,4-cyclohexylene ring, and

denotes a 1,4-phenylene ring.

Above and below “organic group” denotes a carbon or hydrocarbon group.

“Carbon group” denotes a mono- or polyvalent organic group containing at least one carbon atom, where this either contains no further atoms (such as, for example, —C≡C—) or optionally contains one or more further atoms, such as, for example, N, O, S, B, P, Si, Se, As, Te or Ge (for example carbonyl, etc.). The term “hydrocarbon group” denotes a carbon group which additionally contains one or more H atoms and optionally one or more heteroatoms, such as, for example, N, O, S, B, P, Si, Se, As, Te or Ge.

“Halogen” denotes F, Cl, Br or I.

—CO—, —C(═O)— and —C(O)— denote a carbonyl group, i.e.

A carbon or hydrocarbon group can be a saturated or unsaturated group. Unsaturated groups are, for example, aryl, alkenyl or alkynyl groups. A carbon or hydrocarbon radical having more than 3 C atoms can be straight-chain, branched and/or cyclic and may also contain spiro links or condensed rings.

The terms “alkyl”, “aryl”, “heteroaryl”, etc., also encompass polyvalent groups, for example alkylene, arylene, heteroarylene, etc.

The term “aryl” denotes an aromatic carbon group or a group derived therefrom. The term “heteroaryl” denotes “aryl” as defined above, containing one or more heteroatoms, preferably selected from N, O, S, Se, Te, Si and Ge.

Preferred carbon and hydrocarbon groups are optionally substituted, straight-chain, branched or cyclic, alkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to 20, very preferably 1 to 12, C atoms, optionally substituted aryl or aryloxy having 5 to 30, preferably 6 to 25, C atoms, or optionally substituted alkylaryl, arylalkyl, alkylaryloxy, arylalkyloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy having 5 to 30, preferably 6 to 25, C atoms, wherein one or more C atoms may also be replaced by hetero atoms, preferably selected from N, O, S, Se, Te, Si and Ge.

Further preferred carbon and hydrocarbon groups are C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, C₃-C₂₀ allyl, C₄-C₂₀ alkyldienyl, C₄-C₂₀ polyenyl, C₆-C₂₀ cycloalkyl, C₄-C₁₅ cycloalkenyl, C₆-C₃₀ aryl, C₆-C₃₀ alkylaryl, C₆-C₃₀ arylalkyl, C₆-C₃₀ alkylaryloxy, C₆-C₃₀ arylalkyloxy, C₂-C₃₀ heteroaryl, C₂-C₃₀ heteroaryloxy.

Particular preference is given to C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C₆-C₂₅ aryl and C₂-C₂₅ heteroaryl.

Further preferred carbon and hydrocarbon groups are straight-chain, branched or cyclic alkyl having 1 to 20, preferably 1 to 12, C atoms, which are unsubstituted or mono- or polysubstituted by F, Cl, Br, I or CN and in which one or more non-adjacent CH₂ groups may each be replaced, independently of one another,

by —C(R^(x))═C(R^(x))—, —C≡C—, —N(R^(x))—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another.

R^(x) preferably denotes H, F, Cl, CN, a straight-chain, branched or cyclic alkyl chain having 1 to 25 C atoms, in which, in addition, one or more non-adjacent C atoms may be replaced by —O—, —S—, —CO—, —CO—O—, —O—

CO—, —O—CO—O— and in which one or more H atoms may be replaced by F or Cl, or denotes an optionally substituted aryl or aryloxy group with 6 to 30 C atoms, or an optionally substituted heteroaryl or heteroaryloxy group with 2 to 30 C atoms.

Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl, s-pentyl, cyclo-pentyl, n-hexyl, cyclohexyl, 2-ethylhexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecanyl, trifluoromethyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl, perfluorooctyl, perfluorohexyl, etc.

Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl, etc.

Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl, octynyl, etc.

Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxy-ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2-methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n-decoxy, n-undecoxy, n-dodecoxy, etc.

Preferred amino groups are, for example, dimethylamino, methylamino, methylphenylamino, phenylamino, etc.

Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e. they can contain one ring (such as, for example, phenyl) or two or more rings, which may also be fused (such as, for example, naphthyl) or covalently bonded (such as, for example, biphenyl), or contain a combination of fused and linked rings. Heteroaryl groups contain one or more heteroatoms, preferably selected from O, N, S and Se.

Particular preference is given to mono-, bi- or tricyclic aryl groups having 6 to 25 C atoms and mono-, bi- or tricyclic heteroaryl groups having 5 to 25 ring atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6- or 7-membered aryl and heteroaryl groups, in which, in addition, one or more CH groups may be replaced by N, S or O in such a way that O atoms and/or S atoms are not linked directly to one another.

Preferred aryl groups are, for example, phenyl, biphenyl, terphenyl, [1,1′:3′,1″]terphenyl-2′-yl, naphthyl, anthracene, binaphthyl, phenanthrene, 9,10-dihydro-phenanthrene, pyrene, dihydropyrene, chrysene, perylene, tetracene, pentacene, benzopyrene, fluorene, indene, indenofluorene, spirobifluorene, etc.

Preferred heteroaryl groups are, for example, 5-membered rings, such as pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1,2-thiazole, 1,3-thiazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, 6-membered rings, such as pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, 1,2,4-triazine, 1,2,3-triazine, 1,2,4,5-tetrazine, 1,2,3,4-tetrazine, 1,2,3,5-tetrazine, or condensed groups, such as indole, isoindole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphthimidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxalinimidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5,6-quinoline, benzo-6,7-quinoline, benzo-7,8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxazine, benzo-pyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, aza-carbazole, benzocarboline, phenanthridine, phenanthroline, thieno[2,3b]-thiophene, thieno[3,2b]thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene, benzothiadiazothiophene, or combinations of these groups.

The aryl and heteroaryl groups mentioned above and below may also be substituted by alkyl, alkoxy, thioalkyl, fluorine, fluoroalkyl or further aryl or heteroaryl groups.

The (non-aromatic) alicyclic and heterocyclic groups encompass both saturated rings, i.e. those containing exclusively single bonds, and also partially unsaturated rings, i.e. those which may also contain multiple bonds. Heterocyclic rings contain one or more heteroatoms, preferably selected from Si, O, N, S and Se.

The (non-aromatic) alicyclic and heterocyclic groups can be monocyclic, i.e. contain only one ring (such as, for example, cyclohexane), or polycyclic, i.e. contain a plurality of rings (such as, for example, decahydronaphthalene or bicyclooctane). Particular preference is given to saturated groups. Preference is furthermore given to mono-, bi- or tricyclic groups having 5 to 25 ring atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6-, 7- or 8-membered carbocyclic groups, in which, in addition, one or more C atoms may be replaced by Si and/or one or more CH groups may be replaced by N and/or one or more non-adjacent CH₂ groups may be replaced by —O— and/or —S—.

Preferred alicyclic and heterocyclic groups are, for example, 5-membered groups, such as cyclopentane, tetrahydrofuran, tetrahydrothiofuran, pyrrolidine, 6-membered groups, such as cyclohexane, silinane, cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1,3-dioxane, 1,3-dithiane, piperidine, 7-membered groups, such as cycloheptane, and fused groups, such as tetrahydronaphthalene, decahydronaphthalene, indane, bicyclo[1.1.1]-pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl.

Preferred substituents are, for example, solubility-promoting groups, such as alkyl or alkoxy, electron-withdrawing groups, such as fluorine, nitro or nitrile, or substituents for increasing the glass transition temperature (Tg) in the polymer, in particular bulky groups, such as, for example, t-butyl or optionally substituted aryl groups.

Preferred substituents, hereinafter also referred to as “L”, are F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN, —SCN, —C(═O)N(R^(x))₂, —C(═O)Y¹, —C(═O)R^(x), —N(R^(x))₂, straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy each having 1 to 25 C atoms, in which one or more H atoms may optionally be replaced by F or Cl, optionally substituted silyl having 1 to 20 Si atoms, or optionally substituted aryl having 6 to 25, preferably 6 to 15, C atoms,

wherein R^(x) denotes H, F, Cl, CN, or straight chain, branched or cyclic alkyl having 1 to 25 C atoms, wherein one or more non-adjacent CH₂-groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by F, Cl, P- or P-Sp-, and

Y¹ denotes halogen.

“Substituted silyl or aryl” preferably means substituted by halogen, —CN, R⁰, —OR⁰, —CO—R⁰, —CO—O—R⁰, —O—CO—R⁰ or —O—CO—O—R⁰, wherein R⁰ denotes H or alkyl with 1 to 20 C atoms.

Particularly preferred substituents L are, for example, F, Cl, CN, NO₂, CH₃, C₂H₅, OCH₃, OC₂H₅, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅, furthermore phenyl.

is preferably

in which L has one of the meanings indicated above.

The polymerisable group P is a group which is suitable for a polymerisation reaction, such as, for example, free-radical or ionic chain polymerisation, polyaddition or polycondensation, or for a polymer-analogous reaction, for example addition or condensation onto a main polymer chain. Particular preference is given to groups for chain polymerisation, in particular those containing a C═C double bond or —C≡C— triple bond, and groups which are suitable for polymerisation with ring opening, such as, for example, oxetane or epoxide groups.

Preferred groups P are selected from the group consisting of CH₂═CW¹—CO—O—, CH₂═CW¹—CO—,

CH₂═CW²—(O)_(k3)—, CW¹═CH—CO—(O)_(k3)—, CW¹═CH—CO—NH—, CH₂═CW¹—CO—NH—, CH₃—CH═CH—O—, (CH₂═CH)₂CH—OCO—, (CH₂═CH—CH₂)₂CH—OCO—, (CH₂═CH)₂CH—O—, (CH₂═CH—CH₂)₂N—, (CH₂═CH—CH₂)₂N—CO—, HO—CW²W³—, HS—CW²W³—, HW²N—, HO—CW²W³—NH—, CH₂═CW¹—CO—NH—, CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—, CH₂═CH—(CO)_(k1)-Phe-(O)_(k2)—, Phe-CH═CH—, HOOC—, OCN— and W⁴W⁵W⁶Si—, in which W¹ denotes H, F, Cl, CN, CF₃, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, Cl or CH₃, W² and W³ each, independently of one another, denote H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each, independently of one another, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms, W⁷ and W⁸ each, independently of one another, denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene, which is optionally substituted by one or more radicals L as defined above which are other than P-Sp-, k₁, k₂ and k₃ each, independently of one another, denote 0 or 1, k₃ preferably denotes 1, and k₄ denotes an integer from 1 to 10.

Very preferred groups P are selected from the group consisting of CH₂═CW¹—CO—O—, CH₂═CW¹—CO—,

CH₂═CW²—O—, CH₂═CW²—, CW¹═CH—CO—(O)_(k3)—, CW¹═CH—CO—NH—, CH₂═CW¹—CO—NH—, (CH₂═CH)₂CH—OCO—, (CH₂═CH—CH₂)₂CH—OCO—, (CH₂═CH)₂CH—O—, (CH₂═CH—CH₂)₂N—, (CH₂═CH—CH₂)₂N—CO—, CH₂═CW¹—CO—NH—, CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—, CH₂═CH—(CO)_(k1)-Phe-(O)_(k2)—, Phe-CH═CH— and W⁴W⁵W⁶Si—, in which W¹ denotes H, F, Cl, CN, CF₃, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, Cl or CH₃, W² and W³ each, independently of one another, denote H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each, independently of one another, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms, W⁷ and W⁸ each, independently of one another, denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene, k₁, k₂ and k₃ each, independently of one another, denote 0 or 1, k₃ preferably denotes 1, and k₄ denotes an integer from 1 to 10.

Very particularly preferred groups P are selected from the group consisting of CH₂═CW¹—CO—O—, in particular CH₂═CH—CO—O—, CH₂═C(CH₃)—CO—O— and CH₂═CF—CO—O—, furthermore CH₂═CH—O—, (CH₂═CH)₂CH—O—CO—, (CH₂═CH)₂CH—O—,

Further preferred polymerisable groups P are selected from the group consisting of vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide, most preferably from acrylate and methacrylate.

If Sp is different from a single bond, it is preferably of the formula Sp″-X″, so that the respective radical P-Sp- conforms to the formula P-Sp″-X″-, wherein

-   Sp″ denotes alkylene having 1 to 20, preferably 1 to 12, C atoms,     which is optionally mono- or polysubstituted by F, Cl, Br, I or CN     and in which, in addition, one or more non-adjacent CH₂ groups may     each be replaced, independently of one another, by —O—, —S—, —NH—,     —N(R⁰)—, —Si(R⁰R⁰⁰)—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —S—CO—,     —CO—S—, —N(R⁰⁰)—CO—O—, —O—CO—N(R⁰)—, —N(R⁰)—CO—N(R⁰⁰)—, —CH═CH— or     —C≡C— in such a way that O and/or S atoms are not linked directly to     one another, -   X″ denotes —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CO—N(R⁰)—,     —N(R⁰)—CO—, —N(R⁰)—CO—N(R⁰⁰)—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—,     —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —CF₂CH₂—, —CH₂CF₂—, —CF₂CF₂—,     —CH═N—, —N═CH—, —N═N—, —CH═CR⁰—, —CY²═CY³—, —C≡C—, —CH═CH—CO—O—,     —O—CO—CH═CH— or a single bond, -   R⁰ and R⁰⁰ each, independently of one another, denote H or alkyl     having 1 to 20 C atoms, and -   Y² and Y³ each, independently of one another, denote H, F, Cl or CN.

X″ is preferably —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR⁰—, —NR⁰—CO—, —NR⁰—CO—NR⁰⁰— or a single bond.

Typical spacer groups Sp and -Sp″-X″— are, for example, —(CH₂)_(p1)—, —(CH₂CH₂O)_(q1)—CH₂CH₂—, —CH₂CH₂—S—CH₂CH₂—, —CH₂CH₂—NH—CH₂CH₂— or —(SiR⁰R⁰⁰—O)_(p1)—, in which p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R⁰ and R⁰⁰ have the meanings indicated above.

Particularly preferred groups Sp and -Sp″-X″— are —(CH₂)_(p1)—, —(CH₂)_(p1)—O—, —(CH₂)_(p1)—O—CO—, —(CH₂)_(p1)—CO—O—, —(CH₂)_(p1)—O—CO—O—, in which p1 and q1 have the meanings indicated above.

Particularly preferred groups Sp″ are, in each case straight-chain, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethylene-N-methylimino-ethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.

Preferred compounds of formula A are selected of formula A1:

wherein alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and (O) denotes an oxygen atom or a single bond. Very preferred are compounds of formula A1 wherein (O) denotes an oxygen atom and alkyl is methyl, ethyl, propyl, butyl of pentyl or hexyl, which are preferably straight-chained.

Preferably the proportion of compounds of formula A or A1 in the LC medium is from 2 to 35%, very preferably from 3 to 30%, most preferably from 5 to 25%.

Preferably the LC medium contains 1 to 5, preferably 1, 2 or 3 compounds of formula A or A1.

The compounds of formula B are preferably selected of formula B1

wherein alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and (O) denotes an oxygen atom or a single bond. Very preferred are compounds of formula B1 wherein both groups (O) denote an oxygen atom and alkyl is methyl, ethyl, propyl, butyl of pentyl or hexyl, which are preferably straight-chained.

Preferably the proportion of compounds of formula B or B1 in the LC medium is from 0.5 to 20%, very preferably from 1 to 15%, most preferably from 1 to 10%.

Preferably the LC medium contains 1 to 5, preferably 1, 2 or 3 compounds of formula B or B1.

The compounds of formula T are preferably selected of formula T1

wherein alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and (O) denotes an oxygen atom or a single bond. Very preferred are compounds of formula T1 wherein (O) denotes an oxygen atom and alkyl is methyl, ethyl, propyl, butyl of pentyl or hexyl, which are preferably straight-chained.

Preferably the LC medium contains not more than 5% of compounds of formula T or T1.

Preferably the proportion of compounds of formula T or T1 in the LC medium is from 0.1 to 5%, very preferably from 0.5 to 4%.

Preferably the LC medium contains 1 to 5, preferably 1 or 2 compounds of formula T or T1.

In the LC medium according to the present invention, the use of an LC host mixture comprising compounds of formula A, B and T, but not containing any further terphenyl compounds, together with the use of a polymerisable component comprising preferably direactive and/or trireactive RMs, leads to advantageous properties in PSA displays. In particular, one or more of the following advantages could be achieved:

-   -   good UV absorption also at longer wavelengths,     -   quick and complete polymerisation of the RMs,     -   quick generation of a low pretilt angle, especially already at         low UV energy and/or at longer UV wavelengths,     -   high pretilt angle stability after UV exposure,     -   reduced image sticking,     -   reduced ODF mura,     -   high reliability and high VHR value after UV exposure and/or         heat treatment,     -   high birefringence,     -   reduced viscosity     -   faster response times.

Since the LC medium according to the present invention shows high absorption at longer UV wavelengths, it is possible to use longer UV wavelengths for polymerisation, which is advantageous for the display manufacturing process.

The polymerisable compounds are preferably selected from formula I

R^(a)—B¹—(Z^(b)—B²)_(m)—R^(b)  I

in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:

-   R^(a) and R^(b) P, P-Sp-, H, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS,     —OCN, —SCN, SF₅ or straight-chain or branched alkyl having 1 to 25 C     atoms, in which, in addition, one or more non-adjacent CH₂ groups     may each be replaced, independently of one another,     -   by —C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰⁰)—, —O—, —S—, —CO—, —CO—O—,         —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not         linked directly to one another, and in which, in addition, one         or more H atoms may be replaced by F, Cl, Br, I, CN, P or P-Sp-,         where, if B¹ and/or B² contain a saturated C atom, R^(a) and/or         R^(b) may also denote a radical which is spiro-linked to this         saturated C atom, -   wherein at least one of the radicals R^(a) and R^(b) denotes or     contains a group P or P-Sp-, -   P a polymerisable group, -   Sp a spacer group or a single bond, -   B¹ and B² an aromatic, heteroaromatic, alicyclic or heterocyclic     group, preferably having 4 to 25 ring atoms, which may also contain     fused rings, and which is unsubstituted, or mono- or polysubstituted     by L, -   Z^(b) —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—,     —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —(CH₂)_(n1)—,     —CF₂CH₂—, —CH₂CF₂—, —(CF₂)_(n1)—, —CH═CH—, —CF═CF—, —C≡C—,     —CH═CH—COO—, —OCO—CH═CH—, CR⁰R⁰⁰ or a single bond, -   R⁰ and R⁰⁰ each, independently of one another, denote H or alkyl     having 1 to 12 C atoms, -   m denotes 0, 1, 2, 3 or 4, -   n1 denotes 1, 2, 3 or 4, -   L P, P-Sp-, OH, CH₂OH, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN,     —SCN, —C(═O)N(R^(x))₂, —C(═O)Y¹, —C(═O)R^(x), —N(R^(x))₂, optionally     substituted silyl, optionally substituted aryl having 6 to 20 C     atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl,     alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25     C atoms, in which, in addition, one or more H atoms may be replaced     by F, Cl, P or P-Sp-, -   P and Sp have the meanings indicated above, -   Y¹ denotes halogen, -   R^(x) denotes P, P-Sp-, H, halogen, straight-chain, branched or     cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or     more non-adjacent CH₂ groups may be replaced by —O—, —S—, —CO—,     -   —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are         not linked directly to one another, and in which, in addition,         one or more H atoms may be replaced by F, Cl, P or P-Sp-, an         optionally substituted aryl or aryloxy group having 6 to 40 C         atoms, or an optionally substituted heteroaryl or heteroaryloxy         group having 2 to 40 C atoms.

Particularly preferred compounds of the formula I are those in which B¹ and B² each, independently of one another, denote 1,4-phenylene, 1,3-phenylene, naphthalene-1,4-diyl, naphthalene-2,6-diyl, phenanthrene-2,7-diyl, 9,10-dihydro-phenanthrene-2,7-diyl, anthracene-2,7-diyl, fluorene-2,7-diyl, coumarine, flavone, where, in addition, one or more CH groups in these groups may be replaced by N, cyclohexane-1,4-diyl, in which, in addition, one or more non-adjacent CH₂ groups may be replaced by 0 and/or S, 1,4-cyclohexenylene, bicycle[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, piperidine-1,4-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, indane-2,5-diyl or octahydro-4,7-methanoindane-2,5-diyl, where all these groups may be unsubstituted or mono- or polysubstituted by L as defined above.

Particularly preferred compounds of the formula I are those in which B¹ and B² each, independently of one another, denote 1,4-phenylene, 1,3-phenylene, naphthalene-1,4-diyl or naphthalene-2,6-diyl,

Very preferred compounds of formula I are selected from the following formulae:

in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:

-   P¹, P², P³ a vinyloxy, acrylate, methacrylate, fluoroacrylate,     chloroacrylate, oxetane or epoxy group, -   Sp¹, Sp², Sp³ a single bond or a spacer group where, in addition,     one or more of the radicals P¹-Sp¹-, P¹-Sp²- and P³-Sp³- may denote     R^(aa), with the proviso that at least one of the radicals P¹-Sp¹-,     P²-Sp² and P³-Sp³- present is different from R^(aa), -   R^(aa) H, F, Cl, CN or straight-chain or branched alkyl having 1 to     25 C atoms, in which, in addition, one or more non-adjacent CH₂     groups may each be replaced, independently of one another, by     -   C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—,         —O—CO—O— in such a way that O and/or S atoms are not linked         directly to one another, and in which, in addition, one or more         H atoms may be replaced by F, Cl, CN or P¹-Sp¹-, particularly         preferably straight-chain or branched, optionally mono- or         polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl,         alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1         to 12 C atoms (where the alkenyl and alkynyl radicals have at         least two C atoms and the branched radicals have at least three         C atoms), -   R⁰, R⁰⁰ H or alkyl having 1 to 12 C atoms, -   R^(y) and R^(z) H, F, CH₃ or CF₃, -   X¹, X², X³ —CO—O—, —O—CO— or a single bond, -   Z¹ —O—, —CO—, —C(R^(y)R^(z))— or —CF₂CF₂—, -   Z², Z³ —CO—O—, —O—     -   CO—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂— or —(CH₂)_(n)—, where n is         2, 3 or 4, -   L F, Cl, CN or straight-chain or branched, optionally mono- or     polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl,     alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12     C atoms, -   L′, L″ H, F or Cl, -   r 0, 1, 2, 3 or 4, -   s 0, 1, 2 or 3, -   t 0, 1 or 2, -   x 0 or 1.

Especially preferred are compounds of formulae M2 and M13.

Further preferred are trireactive compounds M15 to M30, in particular M17, M18, M19, M22, M23, M24, M25, M29 and M30.

In the compounds of formulae M1 to M30 the group

is preferably

wherein L on each occurrence, identically or differently, has one of the meanings given above or below, and is preferably F, Cl, CN, NO₂, CH₃, C₂H₅, C(CH₃)₃, CH(CH₃)₂, CH₂CH(CH₃)C₂H₅, OCH₃, OC₂H₅, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂, 0C₂F₅ or P-Sp-, very preferably F, Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃, OCF₃ or P-Sp-, more preferably F, Cl, CH₃, OCH₃, COCH₃ oder OCF₃, especially F or CH₃.

Preferred compounds of formulae M1 to M30 are those wherein P¹, P² and P³ denote an acrylate, methacrylate, oxetane or epoxy group, very preferably an acrylate or methacrylate group.

Further preferred compounds of formulae M1 to M30 are those wherein Sp¹, Sp² and Sp³ are a single bond.

Further preferred compounds of formulae M1 to M30 are those wherein one of Sp¹, Sp² and Sp³ is a single bond and another one of Sp¹, Sp² and Sp³ is different from a single bond.

Further preferred compounds of formulae M1 to M30 are those wherein those groups Sp¹, Sp² and Sp³ that are different from a single bond denote —(CH₂)_(s1)—X″—, wherein s1 is an integer from 1 to 6, preferably 2, 3, 4 or 5, and X″ is X″ is the linkage to the benzene ring and is —O—, —O—CO—, —CO—O, —O—CO—O— or a single bond.

Particular preference is given to LC media comprising one, two or three polymerisable compounds of formula I.

Preferably the proportion of compounds of formula I in the LC medium is from 0.01 to 5%, very preferably from 0.05 to 1%, most preferably from 0.1 to 0.5%.

It was observed that, the combination of polymerisable compounds of formulae M1 to M30 with the compounds of formula A, B and T leads to advantageous behaviour of the LC medium, where a quick and complete polymerisation, the quick generation of a low pretilt angle which is stable after UV exposure, at the same time a high reliability and high VHR value after UV exposure can be achieved together with a high birefringence.

Besides, the LC medium shows high absorption at longer UV wavelengths, so that it is possible to use such longer UV wavelengths for polymerisation, which is advantageous for the display manufacturing process.

For the production of PSA displays, the polymerisable compounds contained in the LC medium are polymerised or crosslinked (if one compound contains two or more polymerisable groups) by in-situ polymerisation in the LC medium between the substrates of the LC display, optionally while a voltage is applied to the electrodes.

The structure of the PSA displays according to the invention corresponds to the usual geometry for PSA displays, as described in the prior art cited at the outset. Geometries without protrusions are preferred, in particular those in which, in addition, the electrode on the colour filter side is unstructured and only the electrode on the TFT side has slots. Particularly suitable and preferred electrode structures for PS-VA displays are described, for example, in US 2006/0066793 A1.

A preferred PSA type LC display of the present invention comprises:

-   -   a first substrate including a pixel electrode defining pixel         areas, the pixel electrode being connected to a switching         element disposed in each pixel area and optionally including a         micro-slit pattern, and optionally a first alignment layer         disposed on the pixel electrode,     -   a second substrate including a common electrode layer, which may         be disposed on the entire portion of the second substrate facing         the first substrate, and optionally a second alignment layer,     -   an LC layer disposed between the first and second substrates and         including an LC medium comprising a polymerisable component A         and a liquid crystal component B as described above and below,         wherein the polymerisable component A may also be polymerised.

The first and/or second alignment layer controls the alignment direction of the LC molecules of the LC layer. For example, in PS-VA displays the alignment layer is selected such that it imparts to the LC molecules homeotropic (or vertical) alignment (i.e. perpendicular to the surface) or tilted alignment. Such an alignment layer may for example comprise a polyimide, which may also be rubbed, or may be prepared by a photoalignment method.

The LC layer with the LC medium can be deposited between the substrates of the display by methods that are conventionally used by display manufacturers, for example the so-called one-drop-filling (ODF) method. The polymerisable component of the LC medium is then polymerised for example by UV photopolymerisation. The polymerisation can be carried out in one step or in two or more steps.

The PSA display may comprise further elements, like a colour filter, a black matrix, a passivation layer, optical retardation layers, transistor elements for addressing the individual pixels, etc., all of which are well known to the person skilled in the art and can be employed without inventive skill.

The electrode structure can be designed by the skilled person depending on the individual display type. For example for PS-VA displays a multi-domain orientation of the LC molecules can be induced by providing electrodes having slits and/or bumps or protrusions in order to create two, four or more different tilt alignment directions.

Upon polymerisation the polymerisable compounds form a crosslinked polymer, which causes a certain pretilt of the LC molecules in the LC medium. Without wishing to be bound to a specific theory, it is believed that at least a part of the crosslinked polymer, which is formed by the polymerisable compounds, will phase-separate or precipitate from the LC medium and form a polymer layer on the substrates or electrodes, or the alignment layer provided thereon. Microscopic measurement data (like SEM and AFM) have confirmed that at least a part of the formed polymer accumulates at the LC/substrate interface.

The polymerisation can be carried out in one step. It is also possible firstly to carry out the polymerisation, optionally while applying a voltage, in a first step in order to produce a pretilt angle, and subsequently, in a second polymerisation step without an applied voltage, to polymerise or crosslink the compounds which have not reacted in the first step (“end curing”).

Suitable and preferred polymerisation methods are, for example, thermal or photopolymerisation, preferably photopolymerisation, in particular UV induced photopolymerisation, which can be achieved by exposure of the polymerisable compounds to UV radiation.

Optionally one or more polymerisation initiators are added to the LC medium. Suitable conditions for the polymerisation and suitable types and amounts of initiators are known to the person skilled in the art and are described in the literature. Suitable for free-radical polymerisation are, for example, the commercially available photoinitiators Irgacure651®, Irgacure184®, Irgacure907®, Irgacure369® or Darocure1173® (Ciba AG). If a polymerisation initiator is employed, its proportion is preferably 0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight.

The polymerisable compounds according to the invention are also suitable for polymerisation without an initiator, which is accompanied by considerable advantages, such, for example, lower material costs and in particular less contamination of the LC medium by possible residual amounts of the initiator or degradation products thereof. The polymerisation can thus also be carried out without the addition of an initiator. In a preferred embodiment, the LC medium thus does not contain a polymerisation initiator.

The LC medium may also comprise one or more stabilisers in order to prevent undesired spontaneous polymerisation of the RMs, for example during storage or transport. Suitable types and amounts of stabilisers are known to the person skilled in the art and are described in the literature. Particularly suitable are, for example, the commercially available stabilisers from the Irganox® series (Ciba AG), such as, for example, Irganox® 1076. If stabilisers are employed, their proportion, based on the total amount of RMs or the polymerisable component (component A), is preferably 10-500,000 ppm, particularly preferably 50-50,000 ppm.

The polymerisable compounds of formula I do in particular show good UV absorption in, and are therefore especially suitable for, a process of preparing a PSA display including one or more of the following features:

-   -   the polymerisable medium is exposed to UV light in the display         in a 2-step process, including a first UV exposure step (“UV-1         step”) to generate the tilt angle, and a second UV exposure step         (“UV-2 step”) to finish polymerization,     -   the polymerisable medium is exposed to UV light in the display         generated by an energy-saving UV lamp (also known as “green UV         lamps”). These lamps are characterized by a relative low         intensity ( 1/100- 1/10 of a conventional UV1 lamp) in their         absorption spectra from 300-380 nm, and are preferably used in         the UV2 step, but are optionally also used in the UV1 step when         avoiding high intensity is necessary for the process.     -   the polymerisable medium is exposed to UV light in the display         generated by a UV lamp with a radiation spectrum that is shifted         to longer wavelengths, preferably 340 nm or more, to avoid short         UV light exposure in the PS-VA process.

Both using lower intensity and a UV shift to longer wavelengths protect the organic layer against damage that may be caused by the UV light.

A preferred embodiment of the present invention relates to a process for preparing a PSA display as described above and below, comprising one or more of the following features:

-   -   the polymerisable LC medium is exposed to UV light in a 2-step         process, including a first UV exposure step (“UV-1 step”) to         generate the tilt angle, and a second UV exposure step (“UV-2         step”) to finish polymerization,     -   the polymerisable LC medium is exposed to UV light generated by         a UV lamp having an intensity of from 0.5 mW/cm² to 10 mW/cm² in         the wavelength range from 300-380 nm, preferably used in the UV2         step, and optionally also in the UV1 step,     -   the polymerisable LC medium is exposed to UV light having a         wavelength of 340 nm or more, and preferably 400 nm or less.

This preferred process can be carried out for example by using the desired UV lamps or by using a band pass filter and/or a cut-off filter, which are substantially transmissive for UV light with the respective desired wavelength(s) and are substantially blocking light with the respective undesired wavelengths. For example, when irradiation with UV light of wavelengths λ of 300-400 nm is desired, UV exposure can be carried out using a wide band pass filter being substantially transmissive for wavelengths 300 nm<λ<400 nm. When irradiation with UV light of wavelength λ of more than 340 nm is desired, UV exposure can be carried out using a cut-off filter being substantially transmissive for wavelengths λ>340 nm.

“Substantially transmissive” means that the filter transmits a substantial part, preferably at least 50% of the intensity, of incident light of the desired wavelength(s). “Substantially blocking” means that the filter does not transmit a substantial part, preferably at least 50% of the intensity, of incident light of the undesired wavelengths. “Desired (undesired) wavelength” e.g. in case of a band pass filter means the wavelengths inside (outside) the given range of λ, and in case of a cut-off filter means the wavelengths above (below) the given value of λ.

This preferred process enables the manufacture of displays by using longer UV wavelengths, thereby reducing or even avoiding the hazardous and damaging effects of short UV light components.

UV radiation energy is in general from 6 to 100 J, depending on the production process conditions.

Preferably the LC medium according to the present invention does essentially consist of a polymerisable component A) and an LC component B) (or LC host mixture) as described above and below. However, the LC medium may additionally comprise one or more further components or additives, preferably selected from the list including but not limited to co-monomers, chiral dopants, polymerisation initiators, inhibitors, stabilizers, surfactants, wetting agents, lubricating agents, dispersing agents, hydrophobing agents, adhesive agents, flow improvers, defoaming agents, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes, pigments and nanoparticles.

Preference is given to LC media in which the polymerisable component A) consists exclusively of polymerisable compounds of formula I*.

In another preferred embodiment the polymerisable component A) contains, in addition to the compounds of formula I*, one or more further polymerisable compounds (“co-monomers”), preferably selected from RMs.

Preferably the proportion of the polymerisable component A) in the LC medium is from >0 to <5%, very preferably from >0 to <1%, most preferably from 0.01 to 0.5%.

Preferably the proportion of the LC component B) in the LC medium is from 95 to <100%, very preferably from 99 to <100%.

Besides the polymerisable component A) as described above, the LC media according to the present invention comprise an LC component B), or LC host mixture, comprising one or more, preferably two or more LC compounds which are selected from low-molecular-weight compounds that are unpolymerisable. These LC compounds are selected such that they stable and/or unreactive to a polymerisation reaction under the conditions applied to the polymerisation of the polymerisable compounds.

Examples of these compounds are the aforementioned compounds of formulae A, B and T.

Preference is given to LC media in which the LC component B), or the LC host mixture, has a nematic LC phase, and preferably has no chiral liquid crystal phase.

Preference is furthermore given to achiral compounds of formula I, and to LC media in which the compounds of component A and/or B are selected exclusively from the group consisting of achiral compounds.

The LC component B), or LC host mixture, is preferably a nematic LC mixture.

In a preferred embodiment of the present invention the LC component B), or LC host mixture, of the LC medium comprises, in addition to the compounds of formula A, one or more further mesogenic or LC compounds comprising a straight-chain, branched or cyclic alkenyl group (hereinafter also referred to as “alkenyl compounds”), wherein said alkenyl group is stable to a polymerisation reaction under the conditions used for polymerisation of the polymerisable compounds contained in the LC medium.

These further alkenyl compounds are preferably selected from formula AN and AY

in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:

-   R^(A1) alkenyl having 2 to 9 C atoms or, if at least one of the     rings X, Y and Z denotes cyclohexenyl, also one of the meanings of     R^(A2), -   R^(A2) alkyl having 1 to 12 C atoms, in which, in addition, one or     two non-adjacent CH₂ groups may be replaced by —O—,     -   —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not         linked directly to one another, -   Z^(x) —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CO—O—,     —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O—, or a single bond, preferably     a single bond, -   L¹⁻⁴ H, F, Cl, OCF₃, CF₃, CH₃, CH₂F or CHF₂H, preferably H, F or Cl, -   x 1 or 2, -   z 0 or 1.

Preferred compounds of formula AN and AY are those wherein R^(A2) is selected from ethenyl, propenyl, butenyl, pentenyl, hexenyl and heptenyl.

Further preferred compounds of formula AN and AY are those wherein L¹ and L² denote F, or one of L¹ and L² denotes F and the other denotes Cl, and L³ and L⁴ denote F, or one of L³ and L⁴ denotes F and the other denotes Cl.

The compounds of the formula AN are preferably selected from the following sub-formulae:

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-7 C atoms. Alkenyl and alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

Very preferred compounds of the formula AN are selected from the following sub-formulae:

in which m denotes 1, 2, 3, 4, 5 or 6, i denotes 0, 1, 2 or 3, and R^(b1) denotes H, CH₃ or C₂H₅.

Very particularly preferred compounds of the formula AN are selected from the following sub-formulae:

Most preferred are compounds of formula AN1a2 and AN1a5.

The compounds of the formula AY are preferably selected from the following sub-formulae:

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-7 C atoms. Alkenyl and alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

Very preferred compounds of the formula AY are selected from the following sub-formulae:

in which m and n each, independently of one another, denote 1, 2, 3, 4, 5 or 6, and alkenyl denotes CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

The LC medium preferably comprises no compounds containing a terminal vinyloxy group (—O—CH═CH₂), in particular no compounds of the formula AN or AY in which R^(A1) or R^(A2) denotes or contains a terminal vinyloxy group (—O—CH═CH₂).

In a first preferred embodiment the LC medium contains an LC component B), or LC host mixture, based on compounds with negative dielectric anisotropy. Such LC media are especially suitable for use in PS-VA and PS-UB-FFS displays. Particularly preferred embodiments of such an LC medium are those of sections a)-z) below:

-   a) LC medium which comprises one or more compounds of the formulae     CY and/or PY:

-   -   wherein     -   a denotes 1 or 2,     -   b denotes 0 or 1,

-   -   R¹ and R² each, independently of one another, denote alkyl         having 1 to 12 C atoms, where, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —OCO— or —COO— in such a way that O atoms are not linked         directly to one another, preferably alkyl or alkoxy having 1 to         6 C atoms,     -   Z^(x) and Z^(y) each, independently of one another,         -   denote —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,             —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single             bond, preferably a single bond,     -   L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃,         CF₃, CH₃, CH₂F, CHF₂.     -   Preferably, both L¹ and L² denote F or one of L¹ and L² denotes         F and the other denotes Cl, or both L³ and L⁴ denote F or one of         L³ and L⁴ denotes F and the other denotes Cl.     -   The compounds of the formula CY are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which a denotes 1 or 2, alkyl and alkyl* each, independently         of one another, denote a straight-chain alkyl radical having 1-6         C atoms, and alkenyl denotes a straight-chain alkenyl radical         having 2-6 C atoms, and (O) denotes an oxygen atom or a single         bond. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,         CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—         or CH₃—CH═CH—(CH₂)₂—.     -   The compounds of the formula PY are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl denotes a straight-chain alkenyl radical having 2-6 C         atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl         preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.

-   b) LC medium which additionally comprises one or more compounds of     the following formula:

-   -   in which the individual radicals have the following meanings:

-   -   R³ and R⁴ each, independently of one another, denote alkyl         having 1 to 12 C atoms, in which, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —O—CO— or —CO—O— in such a way that O atoms are not linked         directly to one another,     -   Z^(y) denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,         —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single bond,         preferably a single bond.     -   The compounds of the formula ZK are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl denotes a straight-chain alkenyl radical having 2-6 C         atoms. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,         CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—         or CH₃—CH═CH—(CH₂)₂—.     -   Especially preferred are compounds of formula ZK1.     -   Particularly preferred compounds of formula ZK are selected from         the following sub-formulae:

-   -   wherein the propyl, butyl and pentyl groups are straight-chain         groups.     -   Most preferred are compounds of formula ZK1a.

-   c) LC medium which additionally comprises one or more compounds of     the following formula:

-   -   in which the individual radicals on each occurrence, identically         or differently, have the following meanings:     -   R⁵ and R⁶ each, independently of one another, denote alkyl         having 1 to 12 C atoms, where, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —OCO— or —COO— in such a way that 0 atoms are not linked         directly to one another, preferably alkyl or alkoxy having 1 to         6 C atoms,

and

-   -   e denotes 1 or 2.     -   The compounds of the formula DK are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl denotes a straight-chain alkenyl radical having 2-6 C         atoms. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,         CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—         or CH₃—CH═CH—(CH₂)₂—.

-   d) LC medium which additionally comprises one or more compounds of     the following formula:

-   -   in which the individual radicals have the following meanings:

-   -   with at least one ring F being different from cyclohexylene,     -   f denotes 1 or 2,     -   R¹ and R² each, independently of one another, denote alkyl         having 1 to 12 C atoms, where, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —OCO— or —COO— in such a way that O atoms are not linked         directly to one another,     -   Z^(x) denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,         —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single bond,         preferably a single bond.     -   L¹ and L² each, independently of one another, denote F, Cl,         OCF₃, CF₃, CH₃, CH₂F, CHF₂.     -   Preferably, both radicals L¹ and L² denote F or one of the         radicals L¹ and L² denotes F and the other denotes Cl.     -   The compounds of the formula LY are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which R¹ has the meaning indicated above, alkyl denotes a         straight-chain alkyl radical having 1-6 C atoms, (O) denotes an         oxygen atom or a single bond, and v denotes an integer from 1         to 6. R¹ preferably denotes straight-chain alkyl having 1 to 6 C         atoms or straight-chain alkenyl having 2 to 6 C atoms, in         particular CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, CH₂═CH—,         CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—,         CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

-   e) LC medium which additionally comprises one or more compounds     selected from the group consisting of the following formulae:

-   -   in which alkyl denotes C₁₋₆-alkyl, L^(x) denotes H or F, and X         denotes F, Cl, OCF₃, OCHF₂ or OCH═CF₂. Particular preference is         given to compounds of the formula G1 in which X denotes F.

-   f) LC medium which additionally comprises one or more compounds     selected from the group consisting of the following formulae:

-   -   in which R⁵ has one of the meanings indicated above for R¹,         alkyl denotes C₁₋₆-alkyl, d denotes 0 or 1, and z and m each,         independently of one another, denote an integer from 1 to 6. R⁵         in these compounds is particularly preferably C₁₋₆-alkyl or         -alkoxy or C₂₋₆-alkenyl, d is preferably 1. The LC medium         according to the invention preferably comprises one or more         compounds of the above-mentioned formulae in amounts of ≧5% by         weight.

-   g) LC medium which additionally comprises one or more biphenyl     compounds selected from the group consisting of the following     formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl and alkenyl* each, independently of one another, denote         a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and         alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.     -   The proportion of the biphenyls of the formulae B1 to B3 in the         LC mixture is preferably at least 3% by weight, in particular         ≧5% by weight.     -   The compounds of the formula B2 are particularly preferred.     -   The compounds of the formulae B1 to B3 are preferably selected         from the group consisting of the following sub-formulae:

-   -   in which alkyl* denotes an alkyl radical having 1-6 C atoms. The         medium according to the invention particularly preferably         comprises one or more compounds of the formulae B1a and/or B2c.

-   h) LC medium which additionally comprises one or more compounds     selected from the group consisting of the following formulae:

-   -   in which R¹ and R² have the meanings indicated above and         preferably each, independently of one another, denote         straight-chain alkyl having 1 to 6 C atoms or straight-chain         alkenyl having 2 to 6 C atoms.     -   Preferred media comprise one or more compounds selected from the         formulae O1, O3 and O4.

-   i) LC medium which additionally comprises one or more compounds of     the following formula:

-   -   in which

-   -   R⁹ denotes H, CH₃, C₂H₅ or n-C₃H₇, (F) denotes an optional         fluorine substituent, and q denotes 1, 2 or 3, and R⁷ has one of         the meanings indicated for R¹, preferably in amounts of >3% by         weight, in particular ≧5% by weight and very particularly         preferably 5-30% by weight.     -   Particularly preferred compounds of the formula FI are selected         from the group consisting of the following sub-formulae:

-   -   in which R⁷ preferably denotes straight-chain alkyl, and R⁹         denotes CH₃, C₂H₅ or n-C₃H₇. Particular preference is given to         the compounds of the formulae FI1, FI2 and FI3.

-   k) LC medium which additionally comprises one or more compounds     selected from the group consisting of the following formulae:

-   -   in which R⁸ has the meaning indicated for R¹, and alkyl denotes         a straight-chain alkyl radical having 1-6 C atoms.

-   l) LC medium which additionally comprises one or more compounds     which contain a tetrahydronaphthyl or naphthyl unit, such as, for     example, the compounds selected from the group consisting of the     following formulae:

-   -   in which     -   R¹⁰ and R¹¹ each, independently of one another, denote alkyl         having 1 to 12 C atoms, where, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —OCO— or —COO— in such a way that O atoms are not linked         directly to one another, preferably alkyl or alkoxy having 1 to         6 C atoms,     -   and R¹⁰ and R¹¹ preferably denote straight-chain alkyl or alkoxy         having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C         atoms, and     -   Z¹ and Z² each, independently of one another, denote —C₂H₄—,         —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CH—CH₂CH₂—,         —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—,         —CF═CH—, —CH═CF—, —CH₂— or a single bond.

-   m) LC medium which additionally comprises one or more     difluorodibenzo-chromans and/or chromans of the following formulae:

-   -   in which     -   R¹¹ and R¹² each, independently of one another, have one of the         meanings indicated above for R¹¹,     -   ring M is trans-1,4-cyclohexylene or 1,4-phenylene,     -   Z^(m) —C₂H₄—, —CH₂O—, —OCH₂—, —CO—O— or —O—CO—,     -   c is 0, 1 or 2,     -   preferably in amounts of 3 to 20% by weight, in particular in         amounts of 3 to 15% by weight.     -   Particularly preferred compounds of the formulae BC, CR and RC         are selected from the group consisting of the following         sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, (O)         denotes an oxygen atom or a single bond, c is 1 or 2, and         alkenyl and alkenyl* each, independently of one another, denote         a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and         alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.     -   Very particular preference is given to mixtures comprising one,         two or three compounds of the formula BC-2.

-   n) LC medium which additionally comprises one or more fluorinated     phenanthrenes and/or dibenzofurans of the following formulae:

-   -   in which R¹¹ and R¹² each, independently of one another, have         one of the meanings indicated above for R¹¹, b denotes 0 or 1, L         denotes F, and r denotes 1, 2 or 3.     -   Particularly preferred compounds of the formulae PH and BF are         selected from the group consisting of the following         sub-formulae:

-   -   in which R and R′ each, independently of one another, denote a         straight-chain alkyl or alkoxy radical having 1-7 C atoms.

-   o) LC medium which additionally comprises one or more monocyclic     compounds of the following formula

-   -   wherein     -   R¹ and R² each, independently of one another, denote alkyl         having 1 to 12 C atoms, where, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —OCO— or —COO— in such a way that O atoms are not linked         directly to one another, preferably alkyl or alkoxy having 1 to         6 C atoms,     -   L¹ and L² each, independently of one another, denote F, Cl,         OCF₃, CF₃, CH₃, CH₂F, CHF₂.     -   Preferably, both L¹ and L² denote F or one of L¹ and L² denotes         F and the other denotes Cl,     -   The compounds of the formula Y are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which, Alkyl and Alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, Alkoxy         denotes a straight-chain alkoxy radical having 1-6 C atoms,         Alkenyl and Alkenyl* each, independently of one another, denote         a straight-chain alkenyl radical having 2-6 C atoms, and O         denotes an oxygen atom or a single bond. Alkenyl and Alkenyl*         preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.     -   Particularly preferred compounds of the formula Y are selected         from the group consisting of the following sub-formulae:

-   -   wherein Alkoxy preferably denotes straight-chain alkoxy with 3,         4, or 5 C atoms.

-   p) LC medium which, apart from the polymerisable compounds according     to the invention, in particular of the formula I or sub-formulae     thereof and the comonomers, comprises no compounds which contain a     terminal vinyloxy group (—O—CH═CH₂).

-   q) LC medium which comprises 1 to 5, preferably 1, 2 or 3,     polymerisable compounds, preferably selected from polymerisable     compounds according to the invention, in particular of the formula I     or sub-formulae thereof.

-   r) LC medium in which the proportion of polymerisable compounds, in     particular of the formula I or sub-formulae thereof, in the mixture     as a whole is 0.05 to 5%, preferably 0.1 to 1%.

-   s) LC medium which comprises 1 to 8, preferably 1 to 5, compounds of     the formulae CY1, CY2, PY1 and/or PY2. The proportion of these     compounds in the mixture as a whole is preferably 5 to 60%,     particularly preferably 10 to 35%. The content of these individual     compounds is preferably in each case 2 to 20%.

-   t) LC medium which comprises 1 to 8, preferably 1 to 5, compounds of     the formulae CY9, CY10, PY9 and/or PY10. The proportion of these     compounds in the mixture as a whole is preferably 5 to 60%,     particularly preferably 10 to 35%. The content of these individual     compounds is preferably in each case 2 to 20%.

-   u) LC medium which comprises 1 to 10, preferably 1 to 8, compounds     of the formula ZK, in particular compounds of the formulae ZK1, ZK2     and/or ZK6. The proportion of these compounds in the mixture as a     whole is preferably 3 to 25%, particularly preferably 5 to 45%. The     content of these individual compounds is preferably in each case 2     to 20%.

-   v) LC medium in which the proportion of compounds of the formulae     CY, PY and ZK in the mixture as a whole is greater than 70%,     preferably greater than 80%.

-   w) LC medium in which the LC host mixture contains one or more     compounds containing an alkenyl group, preferably selected from the     group consisting of formula CY, PY and LY, wherein one or both of R¹     and R² denote straight-chain alkenyl having 2-6 C atoms, formula ZK     and DK, wherein one or both of R³ and R⁴ or one or both of R⁵ and R⁶     denote straight-chain alkenyl having 2-6 C atoms, and formula B2 and     B3, very preferably selected from formulae CY15, CY16, CY24, CY32,     PY15, PY16, ZK3, ZK4, DK3, DK6, B2 and B3. The concentration of     these compounds in the LC host mixture is preferably from 2 to 70%,     very preferably from 3 to 55%.

-   x) LC medium which contains one or more, preferably 1 to 5,     compounds selected of formula PY1-PY8, very preferably of formula     PY2. The proportion of these compounds in the mixture as a whole is     preferably 1 to 30%, particularly preferably 2 to 20%. The content     of these individual compounds is preferably in each case 1 to 20%.

In a second preferred embodiment the LC medium contains an LC host mixture based on compounds with positive dielectric anisotropy. Such LC media are especially suitable for use in PS-OCB-, PS-TN-, PS-Posi-VA-, PS-IPS- or PS-FFS-displays.

Particularly preferred is an LC medium of this second preferred embodiment, which contains one or more compounds selected from the group consisting of compounds of formula AA and BB

and optionally contains, in addition to the compounds of formula AA and/or BB, one or more compounds of formula CC

in which the individual radicals have the following meanings:

each, independently of one another, and on each occurrence, identically or differently

each, independently of one another, and on each occurrence, identically or differently

-   R²¹, R³¹, R⁴¹, R⁴² each, independently of one another, alkyl,     alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or     alkenyloxy having 2 to 9 C atoms, all of which are optionally     fluorinated, -   X⁰ F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or     halogenated alkenyl or alkenyloxy having 2 to 6 C atoms, -   Z³¹ —CH₂CH₂—, —CF₂CF₂—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH₂O— or     a single bond, preferably —CH₂CH₂—, —COO—, trans-CH═CH— or a single     bond, particularly preferably —COO—, trans-CH═CH— or a single bond, -   Z⁴¹, Z⁴² —CH₂CH₂—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH₂O—,     —CF₂O—, —C≡C— or a single bond, preferably a single bond, -   L²¹, L²², L³¹, L³² H or F, -   g 0, 1, 2 or 3, -   h 0, 1, 2 or 3.

X⁰ is preferably F, Cl, CF₃, CHF₂, OCF₃, OCHF₂, OCFHCF₃, OCFHCHF₂, OCFHCHF₂, OCF₂CH₃, OCF₂CHF₂, OCF₂CHF₂, OCF₂CF₂CHF₂, OCF₂CF₂CHF₂, OCFHCF₂CF₃, OCFHCF₂CHF₂, OCF₂CF₂CF₃, OCF₂CF₂CClF₂, OCClFCF₂CF₃ or CH═CF₂, very preferably F or OCF₃

The compounds of formula AA are preferably selected from the group consisting of the following formulae:

in which A²¹, R²¹, X⁰, L²¹ and L²² have the meanings given in formula AA, L²³ and L²⁴ each, independently of one another, are H or F, and X⁰ is preferably F. Particularly preferred are compounds of formulae AA1 and AA2.

Particularly preferred compounds of formula AA1 are selected from the group consisting of the following subformulae:

in which R²¹, X⁰, L²¹ and L²² have the meaning given in formula AA1, L²³, L²⁴, L²⁵ and L²⁶ are each, independently of one another, H or F, and X⁰ is preferably F.

Very particularly preferred compounds of formula AA1 are selected from the group consisting of the following subformulae:

In which R²¹ is as defined in formula AA1.

Very preferred compounds of formula AA2 are selected from the group consisting of the following subformulae:

in which R²¹, X⁰, L²¹ and L²² have the meaning given in formula AA2, L²³, L²⁴, L²⁵ and L²⁶ each, independently of one another, are H or F, and X⁰ is preferably F.

Very particularly preferred compounds of formula AA2 are selected from the group consisting of the following subformulae:

in which R²¹ and X⁰ are as defined in formula AA2.

Particularly preferred compounds of formula AA3 are selected from the group consisting of the following subformulae:

in which R²¹, X⁰, L²¹ and L²² have the meaning given in formula AA3, and X⁰ is preferably F.

Particularly preferred compounds of formula AA4 are selected from the group consisting of the following subformulae:

in which R²¹ is as defined in formula AA4.

The compounds of formula BB are preferably selected from the group consisting of the following formulae:

in which g, A³¹, A³², R³¹, X⁰, L³¹ and L³² have the meanings given in formula BB, and X⁰ is preferably F. Particularly preferred are compounds of formulae BB1 and BB2.

Particularly preferred compounds of formula BB1 are selected from the group consisting of the following subformulae:

in which R³¹, X⁰, L³¹ and L³² have the meaning given in formula BB1, and X⁰ is preferably F.

Very particularly preferred compounds of formula BB1a are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB1.

Very particularly preferred compounds of formula BB1 b are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB1.

Particularly preferred compounds of formula BB2 are selected from the group consisting of the following subformulae:

in which R³¹, X⁰, L³¹ and L³² have the meaning given in formula BB2, L³³, L³⁴, L³⁵ and L³⁶ are each, independently of one another, H or F, and X⁰ is preferably F.

Very particularly preferred compounds of formula BB2 are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB2.

Very particularly preferred compounds of formula BB2b are selected from the group consisting of the following subformulae

in which R³¹ is as defined in formula BB2.

Very particularly preferred compounds of formula BB2c are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB2.

Very particularly preferred compounds of formula BB2d and BB2e are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB2.

Very particularly preferred compounds of formula BB2f are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB2.

Very particularly preferred compounds of formula BB2g are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB2.

Very particularly preferred compounds of formula BB2h are selected from the group consisting of the following subformulae:

in which R³¹ and X⁰ are as defined in formula BB2.

Very particularly preferred compounds of formula BB2i are selected from the group consisting of the following subformulae:

in which R³¹ and X⁰ are as defined in formula BB2.

Very particularly preferred compounds of formula BB2k are selected from the group consisting of the following subformulae:

in which R³¹ and X⁰ are as defined in formula BB2.

Alternatively to, or in addition to, the compounds of formula BB1 and/or BB2 the LC media may also comprise one or more compounds of formula BB3 as defined above.

Particularly preferred compounds of formula BB3 are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula BB3.

Preferably the LC media according to this second preferred embodiment comprise, in addition to the compounds of formula AA and/or BB, one or more dielectrically neutral compounds having a dielectric anisotropy in the range from −1.5 to +3, preferably selected from the group of compounds of formula CC as defined above.

Particularly preferred compounds of formula CC are selected from the group consisting of the following subformulae:

In which R⁴¹ and R⁴² have the meanings given in formula CC, and preferably denote each, independently of one another, alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C atoms, and L⁴ is H or F.

Preferably the LC media according to this second preferred embodiment comprise, in addition or alternatively to the dielectrically neutral compounds of formula CC, one or more dielectrically neutral compounds having a dielectric anisotropy in the range from −1.5 to +3, selected from the group of compounds of formula DD.

In which A⁴¹, A⁴², Z⁴¹, Z⁴², R⁴¹, R⁴² and h have the meanings given in formula CC.

Particularly preferred compounds of formula DD are selected from the group consisting of the following subformulae:

in which R⁴¹ and R⁴² have the meanings given in formula DD and R⁴¹ preferably denotes alkyl bedeutet, and in formula DD1 R⁴² preferably denotes alkenyl, particularly preferably —(CH₂)₂—CH═CH—CH₃, and in formula DD2 R⁴² preferably denotes alkyl, —(CH₂)₂—CH═CH₂ or —(CH₂)₂—CH═CH—CH₃.

The compounds of formula AA and BB are preferably used in the LC medium according to the invention in a concentration from 2% to 60%, more preferably from 3% to 35%, and very particularly preferably from 4% to 30% in the mixture as a whole.

The compounds of formula CC and DD are preferably used in the LC medium according to the invention in a concentration from 2% to 70%, more preferably from 5% to 65%, even more preferably from 10% to 60%, and very particularly preferably from 10%, preferably 15%, to 55% in the mixture as a whole.

The combination of compounds of the preferred embodiments mentioned above with the polymerised compounds described above causes low threshold voltages, low rotational viscosities and very good low-temperature stabilities in the LC media according to the invention at the same time as constantly high clearing points and high HR values, and allows the rapid establishment of a particularly low pretilt angle in PSA displays. In particular, the LC media exhibit significantly shortened response times, in particular also the grey-shade response times, in PSA displays compared with the media from the prior art.

The LC media and LC host mixtures of the present invention preferably have a nematic phase range of at least 80 K, particularly preferably at least 100 K, and a rotational viscosity ≦250 mPa·s, preferably ≦200 mPa·s, at 20° C.

In the VA-type displays according to the invention, the molecules in the layer of the LC medium in the switched-off state are aligned perpendicular to the electrode surfaces (homeotropically) or have a a tilted homeotropic alignment. On application of an electrical voltage to the electrodes, a realignment of the LC molecules takes place with the longitudinal molecular axes parallel to the electrode surfaces.

LC media according to the invention based on compounds with negative dielectric anisotropy according to the first preferred embodiment, in particular for use in displays of the PS-VA and PS-UB-FFS type, have a negative dielectric anisotropy Δ∈, preferably from −0.5 to −10, in particular from −2.5 to −7.5, at 20° C. and 1 kHz.

The birefringence Δn in LC media according to the invention for use in displays of the PS-VA and PS-UB-FFS type is preferably below 0.16, particularly preferably from 0.06 to 0.14, very particularly preferably from 0.07 to 0.12.

In the OCB-type displays according to the invention, the molecules in the layer of the LC medium have a “bend” alignment. On application of an electrical voltage, a realignment of the LC molecules takes place with the longitudinal molecular axes perpendicular to the electrode surfaces.

LC media according to the invention for use in displays of the PS-OCB, PS-TN, PS-IPS, PS-posi-VA and PS-FFS type are preferably those based on compounds with positive dielectric anisotropy according to the second preferred embodiment, and preferably have a positive dielectric anisotropy Δ∈ from +4 to +17 at 20° C. and 1 kHz.

The birefringence Δn in LC media according to the invention for use in displays of the PS-OCB type is preferably from 0.14 to 0.22, particularly preferably from 0.16 to 0.22.

The birefringence Δn in LC media according to the invention for use in displays of the PS-TN-, PS-posi-VA-, PS-IPS-oder PS-FFS-type is preferably from 0.07 to 0.15, particularly preferably from 0.08 to 0.13.

LC media according to the invention, based on compounds with positive dielectric anisotropy according to the second preferred embodiment, for use in displays of the PS-TN-, PS-posi-VA-, PS-IPS-oder PS-FFS-type, preferably have a positive dielectric anisotropy Δ∈ from +2 to +30, particularly preferably from +3 to +20, at 20° C. and 1 kHz.

The LC media according to the invention may also comprise further additives which are known to the person skilled in the art and are described in the literature, such as, for example, polymerisation initiators, inhibitors, stabilisers, surface-active substances or chiral dopants. These may be polymerisable or non-polymerisable. Polymerisable additives are accordingly ascribed to the polymerisable component or component A). Non-polymerisable additives are accordingly ascribed to the non-polymerisable component or component B).

In a preferred embodiment the LC media contain one or more chiral dopants, preferably in a concentration from 0.01 to 1%, very preferably from 0.05 to 0.5%. The chiral dopants are preferably selected from the group consisting of compounds from Table B below, very preferably from the group consisting of R- or S-1011, R- or S-2011, R- or S-3011, R- or S-4011, and R- or S-5011.

In another preferred embodiment the LC media contain a racemate of one or more chiral dopants, which are preferably selected from the chiral dopants mentioned in the previous paragraph.

Furthermore, it is possible to add to the LC media, for example, 0 to 15% by weight of pleochroic dyes, furthermore nanoparticles, conductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutyl-ammonium tetraphenylborate or complex salts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq. Cryst. 24, 249-258 (1973)), for improving the conductivity, or substances for modifying the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Substances of this type are described, for example, in DE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430 and 28 53 728.

The individual components of the preferred embodiments a)-z) of the LC media according to the invention are either known or methods for the preparation thereof can readily be derived from the prior art by the person skilled in the relevant art, since they are based on standard methods described in the literature. Corresponding compounds of the formula CY are described, for example, in EP-A-0 364 538. Corresponding compounds of the formula ZK are described, for example, in DE-A-26 36 684 and DE-A-33 21 373.

The LC media which can be used in accordance with the invention are prepared in a manner conventional per se, for example by mixing one or more of the above-mentioned compounds with one or more polymerisable compounds as defined above, and optionally with further liquid-crystalline compounds and/or additives. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing. The invention furthermore relates to the process for the preparation of the LC media according to the invention.

It goes without saying to the person skilled in the art that the LC media according to the invention may also comprise compounds in which, for example, H, N, O, Cl, F have been replaced by the corresponding isotopes like deuterium etc.

The following examples explain the present invention without restricting it. However, they show the person skilled in the art preferred mixture concepts with compounds preferably to be employed and the respective concentrations thereof and combinations thereof with one another. In addition, the examples illustrate which properties and property combinations are accessible.

The following abbreviations are used:

(n, m, z: in each case, independently of one another, 1, 2, 3, 4, 5 or 6)

TABLE A

In a preferred embodiment of the present invention, the LC media according to the invention comprise one or more compounds selected from the group consisting of compounds from Table A.

TABLE B

C 15

CB 15

CM 21

R/S-811

CM 44

CM 45

CM 47

CN

R/S-2011

R/S-3011

R/S-4011

R/S-5011

R/S-1011

Table B shows possible chiral dopants which can be added to the LC media according to the invention.

The LC media preferably comprise 0 to 10% by weight, in particular 0.01 to 5% by weight, particularly preferably 0.1 to 3% by weight, of dopants. The LC media preferably comprise one or more dopants selected from the group consisting of compounds from Table B.

TABLE C

Table C shows possible stabilisers which can be added to the LC media according to the invention.

(n here denotes an integer from 1 to 12, preferably 1, 2, 3, 4, 5, 6, 7 or 8, terminal methyl groups are not shown).

The LC media preferably comprise 0 to 10% by weight, in particular 1 ppm to 5% by weight, particularly preferably 1 ppm to 1% by weight, of stabilisers. The LC media preferably comprise one or more stabilisers selected from the group consisting of compounds from Table C.

TABLE D

RM-1

RM-2

RM-3

RM-4

RM-5

RM-6

RM-7

RM-8

RM-9

RM-10

RM-11

RM-12

RM-13

RM-14

RM-15

RM-16

RM-17

RM-18

RM-19

RM-20

RM-21

RM-22

RM-23

RM-24

RM-25

RM-26

RM-27

RM-28

RM-29

RM-30

RM-31

RM-32

RM-33

RM-34

RM-35

RM-36

RM-37

RM-38

RM-39

RM-40

RM-41

RM-42

RM-43

RM-44

RM-45

RM-46

RM-47

RM-48

RM-49

RM-50

RM-51

RM-52

RM-53

RM-54

RM-55

RM-56

RM-57

RM-58

RM-59

RM-60

RM-61

RM-62

RM-63

RM-64

RM-65

RM-66

RM-67

RM-68

RM-69

RM-70

RM-71

Table D shows illustrative compounds which can be used in the LC media in accordance with the present invention, preferably as reactive mesogenic compounds.

In a preferred embodiment of the present invention, the mesogenic media comprise one or more compounds selected from the group of the compounds from Table D. Very preferably the LC medium comprises a compound selected from formulae RM-1 to RM-32, most preferably RM-1, RM-15 or RM-17, or a compound selected from formulae RM-41 to RM-48, most preferably RM-41.

In addition, the following abbreviations and symbols are used:

-   V₀ threshold voltage, capacitive [V] at 20° C., -   n_(e) extraordinary refractive index at 20° C. and 589 nm, -   n_(o) ordinary refractive index at 20° C. and 589 nm, -   Δn optical anisotropy at 20° C. and 589 nm, -   ∈_(⊥) dielectric permittivity perpendicular to the director at     20° C. and 1 kHz, -   ∈_(∥) dielectric permittivity parallel to the director at 20° C. and     1 kHz, -   Δ∈ dielectric anisotropy at 20° C. and 1 kHz, -   cl.p., T(N,I) clearing point [° C.], -   γ₁ rotational viscosity at 20° C. [mPa·s], -   K₁ elastic constant, “splay” deformation at 20° C. [pN], -   K₂ elastic constant, “twist” deformation at 20° C. [pN], -   K₃ elastic constant, “bend” deformation at 20° C. [pN].

Unless explicitly noted otherwise, all concentrations in the present application are quoted in percent by weight and relate to the corresponding mixture as a whole, comprising all solid or liquid-crystalline components, without solvents.

Unless explicitly noted otherwise, all temperature values indicated in the present application, such as, for example, for the melting point T(C,N), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T(N,I), are quoted in degrees Celsius (° C.). M.p. denotes melting point, cl.p.=clearing point. Furthermore, C=crystalline state, N=nematic phase, S=smectic phase and I=isotropic phase. The data between these symbols represent the transition temperatures.

All physical properties are and have been determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20° C., and Δn is determined at 589 nm and Δ∈ at 1 kHz, unless explicitly indicated otherwise in each case.

The term “threshold voltage” for the present invention relates to the capacitive threshold (V₀), also known as the Freedericks threshold, unless explicitly indicated otherwise. In the examples, the optical threshold may also, as generally usual, be quoted for 10% relative contrast (V₁₀).

Unless stated otherwise, the process of polymerising the polymerisable compounds in the PSA displays as described above and below is carried out at a temperature where the LC medium exhibits a liquid crystal phase, preferably a nematic phase, and most preferably is carried out at room temperature.

Unless stated otherwise, methods of preparing test cells and measuring their electrooptical and other properties are carried out by the methods as described hereinafter or in analogy thereto.

The display used for measurement of the capacitive threshold voltage consists of two plane-parallel glass outer plates at a separation of 25 μm, each of which has on the inside an electrode layer and an unrubbed polyimide alignment layer on top, which effect a homeotropic edge alignment of the liquid-crystal molecules.

The display or test cell used for measurement of the tilt angles consists of two plane-parallel glass outer plates at a separation of 4 μm, each of which has on the inside an electrode layer and a polyimide alignment layer on top, where the two polyimide layers are rubbed antiparallel to one another and effect a homeotropic edge alignment of the liquid-crystal molecules.

The polymerisable compounds are polymerised in the display or test cell by irradiation with UVA light of defined intensity for a prespecified time, with a voltage simultaneously being applied to the display (usually 10 V to 30 V alternating current, 1 kHz). In the examples, unless indicated otherwise, a metal halide lamp and an intensity of 50 mW/cm² is used for polymerisation. The intensity is measured using a standard UVA meter (Hoenle UV-meter high end with UVA sensor).

The tilt angle is determined by crystal rotation experiment (Autronic-Melchers TBA-105). A low value (i.e. a large deviation from the 90° angle) corresponds to a large tilt here.

The VHR value is measured as follows: 0.3% of a polymerisable monomeric compound is added to the LC host mixture, and the resultant mixture is introduced into VA-VHR test cells which comprise an unrubbed VA-polyimide alignment layer. The LC-layer thickness d is approx. 6 μm, unless stated otherwise. The VHR value is determined before and after UV exposure at 1 V, 60 Hz, 64 μs pulse (measuring instrument: Autronic-Melchers VHRM-105).

LC Host Mixtures Example 1

The nematic LC host mixture N1 is formulated as follows.

CC-3-V 35.50% cl.p. 74.7° C. CC-3-V1 10.00% Δn 0.1093 CCP-3-1 2.00% Δε −3.2 CCY-3-O1 2.00% ε_(∥) 3.5 CLY-3-O2 9.50% γ₁ 84 mPa s CPY-2-O2 10.00% CPY-3-O2 10.50% PY-3-O2 16.50% PGIY-3-O2 1.00% B-2O-O5 3.00%

The mixture contains compound CLY-3-O2 of formula A1, compound B-2O-O5 of formula B1, and 1% of terphenyl compound PGIY-2-O4 of formula T1.

Comparison Example 1

The nematic LC host mixture C1 is formulated as follows.

CC-3-V 37.00% cl.p. 75.0° C. CC-3-V1 7.00% Δn 0.1089 CCY-3-O1 5.50% Δε −3.2 CLY-3-O2 10.00% ε_(∥) 3.5 CPY-2-O2 9.50% γ₁ 87 mPa s CPY-3-O2 11 .00% PY-3-O2 19.00% PGIY-2-O4 1.00%

The mixture contains compound CLY-3-O2 of formula A1 and 1% of terphenyl compound PGIY-2-04 of formula T1, but does not contain a compound of formula B.

Example 2

The nematic LC host mixture N2 is formulated as follows.

CC-3-V 37.00% cl.p. 74.6° C. CC-3-V1 10.00% Δn 0.1094 CCY-3-O1 3.50% Δε −3.2 CLY-3-O2 10.00% ε_(∥) 3.6 CPY-2-O2 7.00% γ₁ 85 mPa s CPY-3-O2 11.00% PY-3-O2 16.50% PGIY-3-O2 3.00% B-2O-O5 3.00%

The mixture contains compound CLY-3-O2 of formula A1, compound B-2O-O5 of formula B, and 3% of terphenyl compound PGIY-3-O2 of formula T1.

Comparison Example 2

The nematic LC host mixture C2 is formulated as follows.

CC-3-V 37.00% cl.p. 74.8° C. CC-3-V1 7.00% Δn 0.1094 CCY-3-O1 5.50% Δε −3.2 CLY-3-O2 10.00% ε_(∥) 3.5 CPY-2-O2 8.00% γ₁ 88 mPa s CPY-3-O2 10.50% PY-3-O2 18.50% PGIY-3-O2 3.00%

The mixture contains compound CLY-3-O2 of formula A1 and 3% of terphenyl compound PGIY-3-O2 of formula T1, but does not contain a compound of formula B.

Comparison Example 3

The nematic LC host mixture C3 is formulated as follows.

CC-3-V 32.50% cl.p. 75.2° C. CC-3-V1 10.00% Δn 0.1087 CCP-3-1 4.50% Δε −3.2 CCY-3-O1 9.00% ε_(∥) 3.6 CCY-3-O2 3.00% γ₁ 90 mPa s CPY-2-O2 8.00% CPY-3-O2 11.00% PY-3-O2 18.00% PGIY-3-O2 1.00% B-2O-O5 3.00%

The mixture contains compound B-2O-O5 of formula B1 and 1% of terphenyl compound PGIY-3-O2 of formula T1, but does not contain a compound of formula A.

Comparison Example 4

The nematic LC host mixture C4 is formulated as follows.

CC-3-V 36.00% cl.p. 74.5° C. CC-3-V1 10.50% Δn 0.1094 CCY-3-O1 2.50% Δε −3.2 CLY-3-O2 10.00% ε_(∥) 3.5 CPY-2-O2 10.00% γ₁ 85 mPa s CPY-3-O2 11.00% PY-3-O2 16.00% PYP-2-3 1.00% B-2O-O5 3.00%

The mixture contains compound CLY-3-O2 of formula A1 and compound B-2O-O5 of formula B1, but contains a terphenyl compound PYP-2-3 which is different from formula T.

Comparison Example 5

The nematic LC host mixture C5 is formulated as follows.

CC-3-V 33.00% cl.p. 75.0° C. CC-3-V1 10.00% Δn 0.1084 CCY-3-O1 9.00% Δε −3.2 CCY-3-O2 7.50% ε_(∥) 3.6 CPY-2-O2 5.00% γ₁ 90 mPa s CPY-3-O2 10.50% PY-3-O2 18.00% PYP-2-3 1.00% B-2O-O5 3.00% BCH-32 3.00%

The mixture contains compound B-2O-O5 of formula B1, but does not contain a compound of formula A, and contains a terphenyl compound PYP-2-3 which is different from formula T.

Polymerisable Mixtures

Polymerisable mixtures are prepared by adding either reactive mesogen M1 or M2 to each of nematic LC host mixtures N1, N2 and C1 to C5, respectively, at a concentration of 0.4% by weight.

The composition of the polymerisable mixtures is shown in Table 1 below.

TABLE 1 Polymerisable Mixture Composition Mix. No. LC Host RM P11 N1 M1 P12 N1 M2 P21 N2 M1 C11 C1 M1 C12 C1 M2 C21 C2 M1 C31 C3 M1 C41 C4 M1 C51 C5 M1

The viscosities of polymerisable mixtures with M1 are shown in Table 2.

TABLE 2 Viscosities of Polymerisable Mixtures Mix. No. LC Host RM γ₁ [mPa s] P11 N1 M1 84 P21 N2 M1 85 C11 C1 M1 87 C21 C2 M1 88 C31 C3 M1 90 C41 C4 M1 85 C51 C5 M1 90

It can be seen that the polymerisable mixtures P11 and P21 based on nematic host mixtures N1 and N2 according to the present invention show the lowest viscosities.

Mixture C41, which contains terphenyl compound PYP-2-3 that is different from formula T1, has similar viscosity as mixture P11, but shows inferior polymerisation property as will be shown below.

Use Examples

Each of the polymerisable mixtures according to the invention and the polymerisable comparison mixtures are each inserted into a VA e/o test cell. The test cells comprise a VA-polyimide alignment layer (JALS-2096-R1) which is rubbed antiparallel. The LC-layer thickness d is approx. 4 μm.

For polymerisation of the RMs, unless stated otherwise the test cell is irradiated with UV light using a wide band pass filter (300 nm<λ<400 nm) at 10 J (50 mW/cm²·240 s) with application of a voltage of 14 Vpp (alternating current).

In order to determine the polymerisation rate, the residual content of unpolymerised RM (in % by weight) in the test cells is measured by HPLC after polymerisation. For this purpose the polymerisable mixture is polymerised in the test cell by exposure to UV light (wavelength >320 nm, energy 30 J, exposure time 600 sec). The mixture is then rinsed out of the test cell using MEK (methyl ethyl ketone) and measured.

The residual concentrations of the RM in the mixture after different exposure times are shown in Tables 3-5.

TABLE 3 Residual monomer content Residual RM [%] C11 P11 C21 P21 40 min 0.0659 0.0492 0.0338 0.0310 60 min 0.0366 0.0254 0.0161 0.0137 80 min 0.0260 0.0164 0.0078 0.0075

From Table 3 it can be seen that the polymerisable mixtures P11 (with 1% terphenyl) and P12 (with 3% terphenyl) according to the present invention show faster polymerisation with lower amount of residual RM, compared to the corresponding polymerisable mixtures C11 (with 1% terphenyl) and C12 (with 3% terphenyl) which do not contain a compound of formula B.

TABLE 4 Residual monomer content Residual RM [%] C11 P11 C31 C41 C51 80 min 0.0260 0.0164 0.0138 0.0333 0.0150

From Table 4 it can be seen that polymerisable mixture P11 according to the present invention shows faster polymerisation with a significantly lower amount of residual RM, compared to polymerisable mixture C11 which does not contain a compound of formula B, and polymerisable mixture C41 which contains a terphenyl compound (PYP-2-3) different from formula T.

Polymerisable mixture C31, which does not contain a compound of formula A, and polymerisable mixture C51, which does not contain a compound of formula A and contains a terphenyl compound (PYP-2-3) different from formula T, do both show a slightly lower amount of residual RM than polymerisable mixture P11, but do both have significantly higher viscosity than P11 as shown in Table 2 above.

Overall polymerisable mixture P11 is therefore better suitable for PSA use than C11, C31, C41 and C51.

TABLE 5 Residual monomer content Residual RM [%] C11 P11 C12 P12 80 min 0.0260 0.0164 0.0565 0.0477

From Table 5 it can be seen that the polymerisable mixtures P11 (with M1) and P12 (with M2) according to the present invention show faster polymerisation with significantly lower amount of residual RM, compared to polymerisable mixtures C11 (with M1) and C12 (with M2), which do not contain a compound of formula B. This shows that the host mixture concept of the present invention can be used for different reactive mesogens.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding EP application No. 15000176.6, filed Jan. 22, 2015, are incorporated by reference herein.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. A liquid crystal (LC) medium comprising one or more polymerisable compounds, one or more compounds of formula A, one or more compounds of formula B, and one or more compounds of formula T

in which R¹, R² are, each independently, an alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, and L¹, L², L³ are, each independently, F or Cl.
 2. The LC medium of claim 1, wherein the one or more compounds of formula A are of the following formula:

wherein alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and (O) denotes an oxygen atom or a single bond.
 3. The LC medium of claim 1, wherein the one or more compounds of formula B1 are of the following formula:

wherein alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and (O) denotes an oxygen atom or a single bond.
 4. The LC medium according to claim 1, wherein the one or more compounds of formula T are of formula T1

wherein alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and (O) denotes an oxygen atom or a single bond.
 5. The LC medium according to claim 1, wherein the one or more polymerisable compounds are of formula I R^(a)—B¹—(Z^(b)—B²)_(m)—R^(b)  I in which R^(a) and R^(b) are, each independently, P, P-Sp-, H, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN, —SCN, SF₅ or a straight-chain or branched alkyl having 1 to 25 C atoms, in which one or more non-adjacent CH₂ groups are each optionally replaced, independently of one another, by —C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which one or more H atoms are optionally replaced by F, Cl, Br, I, CN, P or P-Sp-, wherein, if B¹ and/or B² contain a saturated C atom, R^(a) and/or R^(b) also denote a radical which is spiro-linked to said saturated C atom, wherein at least one of the radicals R^(a) and R^(b) denotes or contains a group P or P-Sp-, P is a polymerisable group, Sp is a spacer group or a single bond, B¹ and B² are, each independently, an aromatic, heteroaromatic, alicyclic or heterocyclic group, which optionally contains fused rings, and which is unsubstituted, or mono- or polysubstituted by L, Z^(b) is —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —(CH₂)_(n1)—, —CF₂CH₂—, —CH₂CF₂—, —(CF₂)_(n1)—, —CH═CH—, —CF═CF—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH—, CR⁰R⁰⁰ or a single bond, R⁰ and R⁰⁰ are, each independently, H or alkyl having 1 to 12 C atoms, m is 0, 1, 2, 3 or 4, n1 is 1, 2, 3 or 4, L is P, P-Sp-, OH, CH₂OH, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN, —SCN, —C(═O)N(R^(x))₂, —C(═O)Y¹, —C(═O)R^(x), —N(R^(x))₂, optionally substituted silyl, optionally substituted aryl having 6 to 20 C atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which one or more H atoms are optionally replaced by F, Cl, P or P-Sp-, Y¹ is halogen, and R^(x) is P, P-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which one or more non-adjacent CH₂ groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which one or more H atoms are optionally replaced by F, Cl, P or P-Sp-, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 C atoms.
 6. The LC medium according to claim 5, wherein B¹ and B² each, independently of one another, are 1,4-phenylene, 1,3-phenylene, naphthalene-1,4-diyl, naphthalene-2,6-diyl, phenanthrene-2,7-diyl, 9,10-dihydro-phenanthrene-2,7-diyl, anthracene-2,7-diyl, fluorene-2,7-diyl, coumarine, flavone, where one or more CH groups in these groups are optionally replaced by N, cyclohexane-1,4-diyl, in which one or more non-adjacent CH₂ groups are optionally replaced by O and/or S, 1,4-cyclohexenylene, bicycle[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, piperidine-1,4-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, indane-2,5-diyl or octahydro-4,7-methanoindane-2,5-diyl, where all these groups are optionally unsubstituted or mono- or polysubstituted by L.
 7. The LC medium according to claim 1, wherein the one or more polymerisable compounds are of the following formulae:

in which P¹, P², P³ are, each independently, a vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane or epoxy group, Sp¹, Sp², Sp³ are, each independently, a single bond or a spacer group, where one or more of the radicals P¹-Sp¹-, P¹-Sp²- and P³-Sp³- optionally also denote R^(aa), with the proviso that at least one of the radicals P¹-Sp¹-, P²-Sp² and P³-Sp³- present is different from R^(aa), R^(aa) is H, F, Cl, CN or a straight-chain or branched alkyl having 1 to 25 C atoms, in which one or more non-adjacent CH₂ groups are optionally each replaced, independently of one another, by —C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, or —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which one or more H atoms are optionally replaced by F, Cl, CN or P¹-Sp¹-, R⁰, R⁰⁰ are, each independently, H or alkyl having 1 to 12 C atoms, R^(y) and R^(z) are, each independently, H, F, CH₃ or CF₃, X¹, X², X³ are, each independently, —CO—O—, —O—CO— or a single bond, Z¹ are, each independently, —O—, —CO—, —C(R^(y)R^(z))— or —CF₂CF₂—, Z², Z³ are, each independently, —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —OCF₂— or —(CH₂)_(n)—, n is 2, 3 or 4, L is F, Cl, CN or a straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms, L′, L″ are, each independently, H, F or Cl, r is 0, 1, 2, 3 or 4, s is 0, 1, 2 or 3, t is 0, 1 or 2, and x is 0 or
 1. 8. The LC medium according to claim 1, wherein the one or more polymerisable compounds are of formulae M2 and M13.
 9. The LC medium according to claim 1, comprising a polymerisable component A) comprising one or more polymerisable compounds, and an LC component B) comprising one or more compounds of formula A, one or more compounds of formula B, one or more compounds of formula T, and optionally one or more additional mesogenic or liquid-crystalline compounds.
 10. The LC medium according to claim 1, comprising one or more compounds of formulae AN and AY:

in which

R^(A1) is alkenyl having 2 to 9 C atoms or, if at least one of the rings X, Y and Z denotes cyclohexenyl, also one of the meanings of R^(A2), R^(A2) is alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups are optionally replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, Z^(x) is —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O—, or a single bond, L¹⁻⁴ are, each independently, H, F, Cl, OCF₃, CF₃, CH₃, CH₂F or CHF₂H, x is 1 or 2, and z is 0 or
 1. 11. The LC medium according to claim 1, comprising one or more compounds of formulae CY and PY:

in which a denotes 1 or 2, b denotes 0 or 1,

R¹ and R² each, independently of one another, denote alkyl having 1 to 12 C atoms, where one or two non-adjacent CH₂ groups are optionally replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a way that O atoms are not linked directly to one another, Z^(x) denotes —CH═CH—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —O—, —CH₂—, —CH₂CH₂— or a single bond, and L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃, CF₃, CH₃, CH₂F, or CHF₂.
 12. The LC medium according to claim 1, comprising one or more compounds of formulae ZK and DK:

in which

R³ and R⁴ each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups are optionally replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a way that O atoms are not linked directly to one another, Z^(y) denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —CF═CF— or a single bond, R⁵ and R⁶ each, independently of one another, denote alkyl having 1 to 12 C atoms, where one or two non-adjacent CH₂ groups are optionally replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, and e denotes 1 or
 2. 13. The LC medium according to claim 1, wherein the polymerisable compounds are polymerised.
 14. An LC display comprising an LC medium according to claim
 1. 15. The LC display of claim 14, which is a PSA type display.
 16. The LC display of claim 15, which is a PS-VA, PS-OCB, PS-IPS, PS-FFS, PS-UB-FFS, PS-posi-VA or PS-TN display.
 17. The LC display of claim 15, comprising two substrates, at least one which is transparent to light, an electrode provided on each substrate or two electrodes provided on only one of the substrates, and located between the substrates a layer of the LC medium, wherein the polymerisable compounds are polymerised between the substrates of the display.
 18. A process for the production of an LC display according to claim 17, comprising providing the LC medium between the substrates of the display, and polymerising the polymerisable compounds.
 19. A process of preparing an LC medium according to claim 1, comprising mixing together one or more compounds of formula A, one or more compounds of formula B, one or more compounds of formula T, with one or more polymerisable compounds, and optionally with further LC compounds and/or additives. 